Basic Substitution

Replace the letter with the number, then calculate.

Example: If a = 3, find 2a + 5 = 2(3) + 5 = 11

Negative Numbers

Use brackets when substituting negatives to keep the sign safe.

Example: If x = -2, 3x becomes 3(-2) = -6

Squared Values

Square the value before multiplying by other coefficients.

Using Brackets

On a calculator, always put your substituted number in brackets.

Example: If x = -2, type (-2)² not -2².

With Negative Square Powers

Squaring a negative always gives a POSITIVE result.

Example: If x = -2, x² = (-2)² = 4

Kinematics Formulae

Substitute values into physics-style equations like v = u + at.

Example: u=5, a=2, t=3: v = 5 + (2×3) = 11

Subject of the Formula

Sometimes you must substitute, THEN solve for a different variable.

Example: y = 2x + 1. If y=9, what is x? 9 = 2x + 1 → 2x = 8 → x = 4

Fractional Substitution

Carefully calculate the numerator and denominator separately before dividing.

Rearranging First

Sometimes it is easier to simplify or rearrange an expression before substituting the values in.