substitute

In mathematics, to put values in the place of variables in an algebraic expression or formula. An algebraic expansion or simplification can be checked by substituting simple values for each variable. For example, to check that

x3 + y3 = (x + y)(x2 + y2 − xy)

the value x = 1 and y = 2 might be substituted in both sides of the expression, giving

left-hand side: 13 + 23 = 1 + 8 = 9

right-hand side: (1 + 2)(12 + 22 − 2) = 3 × 3 = 9.

The two sides are the same, so the expansion of x3 + y3 is correct.