# Concept derivation guides

299 concept teaching guides, separate from the 36,000 individual question derivations.

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Concept guide



## [Variables and expressions: a value depends on the assignment, the scope and the number system](/en/derivations/derivation-mko-variable-expression-01/?from=%2Fen%2Fderivations%2F%3Fq%3Dmko-variable-expression)

Let E=x+1, F=(x+1)÷2 and H=Σ_{x=1}^{3}(x+1). (1) In ℤ, evaluate E at x=2 and at x=5 and prove that E has no fixed value independent of x; (2) evaluate F at x=4 in ℚ and in ℤ; (3) evaluate H when x=5 is assigned from outside; (4) decide whether (x+1)+x and 2x+1, and whether x·x and 2x, are equivalent on ℤ; (5) distinguish the expression x+1 from the equation x+1=3 and find the solution set of the equation in ℤ.

Variables and algebraic expressions

derivation-mko-variable-expression-01





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