Explore related knowledge and questions →

Question 3608: Derivatives in Both Composition Orders

On this page
  1. Original question and givens
  2. Definition and scope
  3. Step-by-step derivation
  4. Reverse checks
  5. Result
  6. This question review and source binding

Return to catalogue page 19

← Question derivation index · Original question batch

R0006-03608 · q-20261007-advance-20261009-r04-derivative-rules-0058

Original question and givens

On all R, f has ascending coefficients [-5, 8, 0, 4], constant term first and g has ascending coefficients [2, 1, 2, 1], constant term first. At x=2, give ((f∘g)′,(g∘f)′) in that order. Use reduced positive-denominator fractions, retaining /1 for integers.

  • G001 — On all R, f has ascending coefficients [-5, 8, 0, 4], constant term first and g has ascending coefficients [2, 1, 2, 1], constant term first. At x=2, give ((f∘g)′,(g∘f)′) in that order. Use reduced positive-denominator fractions, retaining /1 for integers.

Definition and scope

Use the original question domain, assumptions and cited MKO definitions. This item has second-context mathematical and bilingual review, with the model, answer and every arithmetic step independently recomputed from the original parameters; the source question remains a candidate.

Step-by-step derivation

S001 · implies

Before

f ascending coefficients=[-5, 8, 0, 4]

After

real polynomials are differentiable;use coefficient identities

Conditions: none

Coefficient k multiplies x^k;real polynomials differentiate termwise and constants have derivative0.Coefficient identities and a candidate comparison at one point are different claims.

Step identifiers and dependencies

Rule: polynomial_derivative_premise · Uses: G001

S002 · calculation

Before

f′ coefficient at degree0 := mul(1, 8)

After

f′ coefficient at degree0 = 8

Conditions: none

Multiply by the original degree and lower it by1;the constant term differentiates to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S001

S003 · calculation

Before

f′ coefficient at degree1 := mul(2, 0)

After

f′ coefficient at degree1 = 0

Conditions: none

Multiply by the original degree and lower it by1;the constant term differentiates to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S002

S004 · calculation

Before

f′ coefficient at degree2 := mul(3, 4)

After

f′ coefficient at degree2 = 12

Conditions: none

Multiply by the original degree and lower it by1;the constant term differentiates to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S003

S005 · calculation

Before

g′ coefficient at degree0 := mul(1, 1)

After

g′ coefficient at degree0 = 1

Conditions: none

Multiply by the original degree and lower it by1;the constant term differentiates to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S004

S006 · calculation

Before

g′ coefficient at degree1 := mul(2, 2)

After

g′ coefficient at degree1 = 4

Conditions: none

Multiply by the original degree and lower it by1;the constant term differentiates to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S005

S007 · calculation

Before

g′ coefficient at degree2 := mul(3, 1)

After

g′ coefficient at degree2 = 3

Conditions: none

Multiply by the original degree and lower it by1;the constant term differentiates to0.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S006

S008 · implies

Before

f(x) ascending coefficients=[-5, 8, 0, 4]

After

evaluate at x=2

Conditions: none

Evaluate ascending coefficients by Horner from the highest nonzero term down;ignoring redundant top zero terms changes neither the function nor the retained original list.

Step identifiers and dependencies

Rule: polynomial_evaluation_order · Uses: G001, S007

S009 · calculation

Before

f(x) Horner multiply before degree2 := mul(4, 2)

After

f(x) Horner multiply before degree2 = 8

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S008

S010 · calculation

Before

f(x) Horner add degree2 := sum(8, 0)

After

f(x) Horner add degree2 = 8

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S009

S011 · calculation

Before

f(x) Horner multiply before degree1 := mul(8, 2)

After

f(x) Horner multiply before degree1 = 16

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S010

S012 · calculation

Before

f(x) Horner add degree1 := sum(16, 8)

After

f(x) Horner add degree1 = 24

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S011

S013 · calculation

Before

f(x) Horner multiply before degree0 := mul(24, 2)

After

f(x) Horner multiply before degree0 = 48

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S012

S014 · calculation

Before

f(x) Horner add degree0 := sum(48, -5)

After

f(x) Horner add degree0 = 43

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S013

S015 · implies

Before

g(x) ascending coefficients=[2, 1, 2, 1]

After

evaluate at x=2

Conditions: none

Evaluate ascending coefficients by Horner from the highest nonzero term down;ignoring redundant top zero terms changes neither the function nor the retained original list.

Step identifiers and dependencies

Rule: polynomial_evaluation_order · Uses: G001, S014

S016 · calculation

Before

g(x) Horner multiply before degree2 := mul(1, 2)

After

g(x) Horner multiply before degree2 = 2

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S015

S017 · calculation

Before

g(x) Horner add degree2 := sum(2, 2)

After

g(x) Horner add degree2 = 4

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S016

S018 · calculation

Before

g(x) Horner multiply before degree1 := mul(4, 2)

After

g(x) Horner multiply before degree1 = 8

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S017

S019 · calculation

Before

g(x) Horner add degree1 := sum(8, 1)

After

g(x) Horner add degree1 = 9

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S018

S020 · calculation

Before

g(x) Horner multiply before degree0 := mul(9, 2)

After

g(x) Horner multiply before degree0 = 18

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S019

S021 · calculation

Before

g(x) Horner add degree0 := sum(18, 2)

After

g(x) Horner add degree0 = 20

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S020

S022 · implies

Before

f′(x) ascending coefficients=[8, 0, 12]

After

evaluate at x=2

Conditions: none

Evaluate ascending coefficients by Horner from the highest nonzero term down;ignoring redundant top zero terms changes neither the function nor the retained original list.

Step identifiers and dependencies

Rule: polynomial_evaluation_order · Uses: G001, S021

S023 · calculation

Before

f′(x) Horner multiply before degree1 := mul(12, 2)

After

f′(x) Horner multiply before degree1 = 24

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S022

S024 · calculation

Before

f′(x) Horner add degree1 := sum(24, 0)

After

f′(x) Horner add degree1 = 24

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S023

S025 · calculation

Before

f′(x) Horner multiply before degree0 := mul(24, 2)

After

f′(x) Horner multiply before degree0 = 48

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S024

S026 · calculation

Before

f′(x) Horner add degree0 := sum(48, 8)

After

f′(x) Horner add degree0 = 56

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S025

S027 · implies

Before

g′(x) ascending coefficients=[1, 4, 3]

After

evaluate at x=2

Conditions: none

Evaluate ascending coefficients by Horner from the highest nonzero term down;ignoring redundant top zero terms changes neither the function nor the retained original list.

Step identifiers and dependencies

Rule: polynomial_evaluation_order · Uses: G001, S026

S028 · calculation

Before

g′(x) Horner multiply before degree1 := mul(3, 2)

After

g′(x) Horner multiply before degree1 = 6

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S027

S029 · calculation

Before

g′(x) Horner add degree1 := sum(6, 4)

After

g′(x) Horner add degree1 = 10

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S028

S030 · calculation

Before

g′(x) Horner multiply before degree0 := mul(10, 2)

After

g′(x) Horner multiply before degree0 = 20

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S029

S031 · calculation

Before

g′(x) Horner add degree0 := sum(20, 1)

After

g′(x) Horner add degree0 = 21

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S030

S032 · implies

Before

f′(g(x)) ascending coefficients=[8, 0, 12]

After

evaluate at x=20

Conditions: none

Evaluate ascending coefficients by Horner from the highest nonzero term down;ignoring redundant top zero terms changes neither the function nor the retained original list.

Step identifiers and dependencies

Rule: polynomial_evaluation_order · Uses: G001, S031

S033 · calculation

Before

f′(g(x)) Horner multiply before degree1 := mul(12, 20)

After

f′(g(x)) Horner multiply before degree1 = 240

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S032

S034 · calculation

Before

f′(g(x)) Horner add degree1 := sum(240, 0)

After

f′(g(x)) Horner add degree1 = 240

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S033

S035 · calculation

Before

f′(g(x)) Horner multiply before degree0 := mul(240, 20)

After

f′(g(x)) Horner multiply before degree0 = 4800

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S034

S036 · calculation

Before

f′(g(x)) Horner add degree0 := sum(4800, 8)

After

f′(g(x)) Horner add degree0 = 4808

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S035

S037 · implies

Before

g′(f(x)) ascending coefficients=[1, 4, 3]

After

evaluate at x=43

Conditions: none

Evaluate ascending coefficients by Horner from the highest nonzero term down;ignoring redundant top zero terms changes neither the function nor the retained original list.

Step identifiers and dependencies

Rule: polynomial_evaluation_order · Uses: G001, S036

S038 · calculation

Before

g′(f(x)) Horner multiply before degree1 := mul(3, 43)

After

g′(f(x)) Horner multiply before degree1 = 129

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S037

S039 · calculation

Before

g′(f(x)) Horner add degree1 := sum(129, 4)

After

g′(f(x)) Horner add degree1 = 133

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S038

S040 · calculation

Before

g′(f(x)) Horner multiply before degree0 := mul(133, 43)

After

g′(f(x)) Horner multiply before degree0 = 5719

Conditions: none

Multiply by the same evaluation point first.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S039

S041 · calculation

Before

g′(f(x)) Horner add degree0 := sum(5719, 1)

After

g′(f(x)) Horner add degree0 = 5720

Conditions: none

Then add the full coefficient at this position.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S040

S042 · calculation

Before

(f∘g)′(x) := mul(4808, 21)

After

(f∘g)′(x) = 100968

Conditions: none

Evaluate the outer derivative f′ at g(x),then multiply by the inner derivative g′(x).

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S041

S043 · calculation

Before

(g∘f)′(x) := mul(5720, 56)

After

(g∘f)′(x) = 320320

Conditions: none

The reverse order changes the outer function,the evaluation point and the inner derivative.

Step identifiers and dependencies

Rule: exact_rational_arithmetic · Uses: G001, S042

S044 · implies

Before

inner values=(20,43);inner derivatives=(21,56)

After

ordered derivative values=(100968/1, 320320/1)

Conditions: none

The entries are f after g and g after f in that order;do not swap them.A constant outer function naturally makes its corresponding composite derivative0.

Step identifiers and dependencies

Rule: chain_rule_order_guard · Uses: G001, S043

Reverse checks

  • S044 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S043 · premise_and_result_audit — Recompute (g∘f)′(x) with exact rational arithmetic, not rounded decimals.
  • S042 · premise_and_result_audit — Recompute (f∘g)′(x) with exact rational arithmetic, not rounded decimals.
  • S041 · premise_and_result_audit — Recompute g′(f(x)) Horner add degree0 with exact rational arithmetic, not rounded decimals.
  • S040 · premise_and_result_audit — Recompute g′(f(x)) Horner multiply before degree0 with exact rational arithmetic, not rounded decimals.
  • S039 · premise_and_result_audit — Recompute g′(f(x)) Horner add degree1 with exact rational arithmetic, not rounded decimals.
  • S038 · premise_and_result_audit — Recompute g′(f(x)) Horner multiply before degree1 with exact rational arithmetic, not rounded decimals.
  • S037 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S036 · premise_and_result_audit — Recompute f′(g(x)) Horner add degree0 with exact rational arithmetic, not rounded decimals.
  • S035 · premise_and_result_audit — Recompute f′(g(x)) Horner multiply before degree0 with exact rational arithmetic, not rounded decimals.
  • S034 · premise_and_result_audit — Recompute f′(g(x)) Horner add degree1 with exact rational arithmetic, not rounded decimals.
  • S033 · premise_and_result_audit — Recompute f′(g(x)) Horner multiply before degree1 with exact rational arithmetic, not rounded decimals.
  • S032 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S031 · premise_and_result_audit — Recompute g′(x) Horner add degree0 with exact rational arithmetic, not rounded decimals.
  • S030 · premise_and_result_audit — Recompute g′(x) Horner multiply before degree0 with exact rational arithmetic, not rounded decimals.
  • S029 · premise_and_result_audit — Recompute g′(x) Horner add degree1 with exact rational arithmetic, not rounded decimals.
  • S028 · premise_and_result_audit — Recompute g′(x) Horner multiply before degree1 with exact rational arithmetic, not rounded decimals.
  • S027 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S026 · premise_and_result_audit — Recompute f′(x) Horner add degree0 with exact rational arithmetic, not rounded decimals.
  • S025 · premise_and_result_audit — Recompute f′(x) Horner multiply before degree0 with exact rational arithmetic, not rounded decimals.
  • S024 · premise_and_result_audit — Recompute f′(x) Horner add degree1 with exact rational arithmetic, not rounded decimals.
  • S023 · premise_and_result_audit — Recompute f′(x) Horner multiply before degree1 with exact rational arithmetic, not rounded decimals.
  • S022 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S021 · premise_and_result_audit — Recompute g(x) Horner add degree0 with exact rational arithmetic, not rounded decimals.
  • S020 · premise_and_result_audit — Recompute g(x) Horner multiply before degree0 with exact rational arithmetic, not rounded decimals.
  • S019 · premise_and_result_audit — Recompute g(x) Horner add degree1 with exact rational arithmetic, not rounded decimals.
  • S018 · premise_and_result_audit — Recompute g(x) Horner multiply before degree1 with exact rational arithmetic, not rounded decimals.
  • S017 · premise_and_result_audit — Recompute g(x) Horner add degree2 with exact rational arithmetic, not rounded decimals.
  • S016 · premise_and_result_audit — Recompute g(x) Horner multiply before degree2 with exact rational arithmetic, not rounded decimals.
  • S015 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S014 · premise_and_result_audit — Recompute f(x) Horner add degree0 with exact rational arithmetic, not rounded decimals.
  • S013 · premise_and_result_audit — Recompute f(x) Horner multiply before degree0 with exact rational arithmetic, not rounded decimals.
  • S012 · premise_and_result_audit — Recompute f(x) Horner add degree1 with exact rational arithmetic, not rounded decimals.
  • S011 · premise_and_result_audit — Recompute f(x) Horner multiply before degree1 with exact rational arithmetic, not rounded decimals.
  • S010 · premise_and_result_audit — Recompute f(x) Horner add degree2 with exact rational arithmetic, not rounded decimals.
  • S009 · premise_and_result_audit — Recompute f(x) Horner multiply before degree2 with exact rational arithmetic, not rounded decimals.
  • S008 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
  • S007 · premise_and_result_audit — Recompute g′ coefficient at degree2 with exact rational arithmetic, not rounded decimals.
  • S006 · premise_and_result_audit — Recompute g′ coefficient at degree1 with exact rational arithmetic, not rounded decimals.
  • S005 · premise_and_result_audit — Recompute g′ coefficient at degree0 with exact rational arithmetic, not rounded decimals.
  • S004 · premise_and_result_audit — Recompute f′ coefficient at degree2 with exact rational arithmetic, not rounded decimals.
  • S003 · premise_and_result_audit — Recompute f′ coefficient at degree1 with exact rational arithmetic, not rounded decimals.
  • S002 · premise_and_result_audit — Recompute f′ coefficient at degree0 with exact rational arithmetic, not rounded decimals.
  • S001 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.

Result

(100968/1, 320320/1)

The full substitutions and premise checks give the original answer; source identity,format and status are unchanged.

This question review and source binding

Review date: 2026-10-26

Original questions, answers, step expressions, numeric ASTs and historical records are retained. Source candidate labels remain historical and are not overwritten as formal proof.

Source hashes and review receipts
  • input commit: 0f7be61e2c22317a4075561dc822c87d881a50db
  • original question SHA-256: 55e2a8c8b4658670926364b9852fbe0127256493acf54d9cbdfc9690ba24fbfb
  • candidate record SHA-256: ebffb539a2cf0766701b03a2484c2f827afd73ab4e333ddcbd36459b71731097
  • semantic review receipt SHA-256: 568eefd71709ac3dc16a0d5b3b4ad3e83376a8ef300c9e5493eee0721500b29d
  • question-first witness SHA-256: d964b91bedb9d4918bbc055f567762a09f5a58af6c876268e719d5100332d855
  • Lean: NOT_RUN · human review: NOT_PERFORMED
Same-source full JSON