x pangkat 2 min 9x + 20=0

x^2 - 9x + 20 = 0
(x-5) (x-4) = 0 (difaktorkan)
x-5 = 0
x = 5
atau
x-4 = 0
x = 4

(x-5) (x-4)
x-5=0
x-4=0
x = 5 atau x = 4