Question

f(x) = (x + 5)(x - 4)

Answer 1

F(x)= х^2 -4x +5x - 20
x^2 + x - 20=0
D= 1- 4 * ( -20) = 81= 9^2
x1= -5
x2= 4

Answer 2

(x+5)(x-4)=0
x+5=0 или х-4=0
х=-5           х=4