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
