Jika f(x)=2x+3 dan g(x)=9-x, nilai dr (fog) -¹(-9)

Fog (x)=2(9-x)+3
=18-2x+3
=-2x+21
Fog-1 (x)=
-2x+21=y
-2x=y-21
=(21-y)/2
=(21-x)/2
Fog-1(-9)= (21--9)/2
=15