Question

seja a função f(x) = (x+2) . (x-4), encontre: f(x)= -5

Answer 1

f(x)=(x+2)(x-4)=-5
y=x²-4x+2x-8=-5
y=x²-2x-8+5
y=x²-2x-3

agora calcula o valor de delta 
A=(-2)²-4.1.(-3)
A=4+12
A=16

agora as raizes de delta 

x=-(-2)+-4/2.1
x'=2+4/2
x'=6/2
x'=3

x"=2-4/2
x"=-2/2
x"=-1