Question

Solve the following equations by factorizing:

1) x² + 8x + 15 = 0
2) x² - 7x + 12 = 0
3) x² + 2x - 15 = 0
4) x² - 11x + 28 = 0
5) x² - x - 30 = 0
6) x² + 11x - 26 = 0
7) x² - 5x - 24 = 0
8) 14 + x² + 9x = 0
9) 7 + x² - 18x = -25
10) x² = 17x - 72

Answer 1

1) x² + 8x + 15 = 0

Now what multiples to 15 and adds to 8? 5 and 3, 5x3=15, 5+3=8

so its

(x+5)(x+3)=0

now solve

x+5=0 x+3 =0

x = -5 x = -3

so the solution is -5, -3

4) x² - 11x + 28 = 0

what multiples to 28 and adds to -11? -7 and -4

(x-7)(x-4) =0

x= 7, 4

10) x² = 17x - 72 (okay ill do 3 of them)

first get numbers on same side where x² is positive

x² -17x + 72 = 0

what multiples to 72 and adds to -17? -9 and -8

(x-9)(x-8)=0

x= 9, 8