Understand Algebraic Substitution with Squares and Square Roots

When we substitute a number for a letter, we simply replace the letter with the number.

However, we must remember that 4b means 4 × b and 4b² means 4 × b × b.

Example

Work out the value of the following expression when a = 4 and b = 9

3a² - 7 - 2√b

Answer

3a² - 7 - 2√b

= 3 × a × a - 7 - 2 × √b

= 3 × 4 × 4 - 7 - 2 × √9

= 48 - 7 - 2 × 3

= 48 - 7 - 6

= 35

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