Question 8535: Finite Difference Quotient at a Specified Nonzero Step

Original question and givens

On all R, f(t)=(-9)t²+(-3)t+(18), allowing a2=0. At x=2 and nonzero finite h=-1, compute (f(x+h)−f(x))/h. Give a reduced fraction with positive denominator, retaining /1 for integers.

• G001 — On all R, f(t)=(-9)t²+(-3)t+(18), allowing a2=0. At x=2 and nonzero finite h=-1, compute (f(x+h)−f(x))/h. Give a reduced fraction with positive denominator, 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.

• mko-derivative

Step-by-step derivation

declared real formula on all R;derivative means the two-sided h->0 quotient limit

finite-step evaluation and derivative existence are separate

at original x a*x := mul(-9, 2)

at original x a*x = -18

at original x a*x+b := sum(-18, -3)

at original x a*x+b = -21

at original x (a*x+b)*x := mul(-21, 2)

at original x (a*x+b)*x = -42

at original x f(x) := sum(-42, 18)

at original x f(x) = -24

f(t)=(-9)*t^2+(-3)*t+(18);x=2;f(x)=-24;h!=0

f(x+h)-f(x)=h*(2*(-9)*(2)+(-3)+(-9)*h)

twice quadratic coefficient := mul(2, -9)

twice quadratic coefficient = -18

twice a times x := mul(-18, 2)

twice a times x = -36

linear part of quotient := sum(-36, -3)

linear part of quotient = -39

shifted input x+h := sum(2, -1)

shifted input x+h = 1

at shifted x a*x := mul(-9, 1)

at shifted x a*x = -9

at shifted x a*x+b := sum(-9, -3)

at shifted x a*x+b = -12

at shifted x (a*x+b)*x := mul(-12, 1)

at shifted x (a*x+b)*x = -12

at shifted x f(x) := sum(-12, 18)

at shifted x f(x) = 6

finite increment f(x+h)-f(x) := sub(6, -24)

finite increment f(x+h)-f(x) = 30

specified finite quotient := div(30, -1)

specified finite quotient = -30

finite-step quadratic correction := mul(-9, -1)

finite-step quadratic correction = 9

expanded finite quotient := sum(-39, 9)

expanded finite quotient = -30

finite quotient minus derivative := sub(-30, -39)

finite quotient minus derivative = 9

h=-1;finite quotient=-30/1;derivative value=-39

difference=9;a2*h=9

Reverse checks

• S020 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
• S019 · premise_and_result_audit — Recompute finite quotient minus derivative with exact rational arithmetic, not rounded decimals.
• S018 · premise_and_result_audit — Recompute expanded finite quotient with exact rational arithmetic, not rounded decimals.
• S017 · premise_and_result_audit — Recompute finite-step quadratic correction with exact rational arithmetic, not rounded decimals.
• S016 · premise_and_result_audit — Recompute specified finite quotient with exact rational arithmetic, not rounded decimals.
• S015 · premise_and_result_audit — Recompute finite increment f(x+h)-f(x) with exact rational arithmetic, not rounded decimals.
• S014 · premise_and_result_audit — Recompute at shifted x f(x) with exact rational arithmetic, not rounded decimals.
• S013 · premise_and_result_audit — Recompute at shifted x (a*x+b)*x with exact rational arithmetic, not rounded decimals.
• S012 · premise_and_result_audit — Recompute at shifted x a*x+b with exact rational arithmetic, not rounded decimals.
• S011 · premise_and_result_audit — Recompute at shifted x a*x with exact rational arithmetic, not rounded decimals.
• S010 · premise_and_result_audit — Recompute shifted input x+h with exact rational arithmetic, not rounded decimals.
• S009 · premise_and_result_audit — Recompute linear part of quotient with exact rational arithmetic, not rounded decimals.
• S008 · premise_and_result_audit — Recompute twice a times x with exact rational arithmetic, not rounded decimals.
• S007 · premise_and_result_audit — Recompute twice quadratic coefficient with exact rational arithmetic, not rounded decimals.
• S006 · premise_and_result_audit — Check against the original data and this step's premises; a one-way implication is not an equivalence.
• S005 · premise_and_result_audit — Recompute at original x f(x) with exact rational arithmetic, not rounded decimals.
• S004 · premise_and_result_audit — Recompute at original x (a*x+b)*x with exact rational arithmetic, not rounded decimals.
• S003 · premise_and_result_audit — Recompute at original x a*x+b with exact rational arithmetic, not rounded decimals.
• S002 · premise_and_result_audit — Recompute at original x a*x 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

-30/1

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.