9.5 Multiplication with the Addition-or-Subtraction Method

• Purpose: To use multiplication on linear equations before you add or subtract.

• Homework: p. 432 1-23 odd

• Review Homework: p. 433 (Mixed) #3,5,9,11,13,23,27 AND p. 434 problems 1-25 odd.

Solve.

• 6x + y = 6 ****Notice you can’t eliminate• 3x + 2y = 9 a variable.• Multiply the bottom equation by -2.• 6x + y = 6• -6x + (-4y) = -18 ***NOW ADD.• -3y = -12; y = 4; ***Plug in y.• 6x + 4 = 6; 6x = 2; x = 1/3• (1/3, 4) is the solution

Solve

• 4s – 5t = 3 ****You need to multiply both

• 3s + 2t = -15 equations to eliminate.

• 8s – 10t = 6 **Multiplied by 2.

• 15s + 10t = -75**Multiplied by 5.

• 23s = -69; s = -3 ***Find t.

• -9 + 2t = -15; 2t = -6; t = -3

• (-3, -3) is the solution.