Substitution into an algebraic expression is the process of replacing a letter with a number, in a given algebraic expression. The letters are called variables because they can be replaced by any value.
Example
If x = 2 and y = 3
Find the following:
i. \( \scriptsize x \: + \: 6 \)
ii. \( \scriptsize 4 \: + \: x \: + \: y \)
iii. \( \scriptsize y \: – \: x \)
iv. \( \scriptsize 10 \: – \: 2y \: – \: 3 \)
Solution
i. \( \scriptsize x + 6 \\ = \scriptsize 2 + 6 = \scriptsize 8 \)
ii. \( \scriptsize 4 + x + y \\ = \scriptsize 4 + 2 + 3 = \scriptsize 9 \)
iii. \( \scriptsize y \: – \: x \\ = \scriptsize 3 \: – \: 2 = \scriptsize 1 \)
iv. \( \scriptsize 10 \: – \: 2y \: – \: 3 \\ = \scriptsize 10 \: – \: 2(3) \: – \: 3 \\ = \scriptsize 10 \: – \: 6 \: – \: 3 = \scriptsize 1\)
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