Jika fungsi g(x)=2x-4 dan (gof)(x)=4x2-20x+26, nilai f(-1)=

(gof) (x) = 4x²-20x+26
2f(x) - 4 = 4x²-20x+26
2f(x) = 4x²-20x+26+4
f(x) = 4x²-20x+30 / 2
f(x) = 2x²-10x+15

jadi nilai
f(-1)=2(-1)²-10(-1)+15
=2+10+15
=27