jika f(x) = 2x-1 dan (g o f)(x) = 4x^2 + 2x - 1. maka g(x)?

(g•f)(x)=4x²+2x-1
g(f(x))=4x²+2x-1
g(2x-1)=4x²+2x-1
misalkan a=2x-1,maka x=a+1/2
g(x)=4x²+2x-1
g(a)=4(a+1/2)²+2(a+1/2)-1
g(a)=4(a²+2a+1/4)+2a+2/2-1
g(a)=4a²+2a+1/4)+2a+2/2-1
g(a)=4a²+2a+1+4a+2-4/4
g(a)=4a²+2a+4a+1+2-4/4
g(a)=4a²+6a-1/4
g(a)=a²+1½a-¼
g(x)=x²+1½x-¼