f(x)=x²-2x-4 g(x)=3x+9 (g○f)(a)=6 Tentukan nilai a

[tex] (gof)(a) = 3( {x}^{2} - 2x - 4) + 9 \\ 6 = {3x}^{2} - 6x - 12 + 9 \\ 0 = {3x}^{2} - 6x - 9 \\ 0 = {x}^{2} - 2x - 3 \\ (x - 3)(x + 1) \\ x = 3 \: atau \: x = - 1[/tex]