Evaluating Expressions by Substitution Examples

What's the value of the expression 5x + 11 when x = 3?

Substituting 3 for x produces the new expression 5(3) + 11. Simplifying this new expression gives us 15 + 11 = 26. Boom.

What's the value of 3y² + 3y if y = 2?

Substitute 2 for y to find that 3(2)² + 3(2) = 3(4) + 6. Then work out the arithmetic to find that 12 + 6 = 18 .

If y = -4, what's the value of the expression 2y + y²?

Substitute -4 for y to get 2(-4) + (-4)². Simplify to find that -8 + 16 = 8.