Evaluating Expressions and Solving Equations

To evaluate a variable expression, substitute a number for each variable. Then find the value of the numerical expression.

If x = -6 then 6x = ? matches -36.

“6 times -6 is -36.”

To solve an equation, use inverse operations. Whatever operation is done to one side of the equation must be done to the other side to make an equivalent equation.

If a = b, then a + c = b + c.

If a = b, then a - c = b - c.

If a = b, then ac = bc.

If a = b, and c ≠ 0, then a / c = b / c.

n - 8 = 12  matches n = 20.

“If you add 8 to both sides, then n = 20.”

Warm-Up

2n + 3 = 15 matches n = 6.

“First subtract 3 from each side to get 2n = 12. Then divide both sides by 2 to get n = 6.”