Jika (f○g)(x)=5x-1 dan g(x) = 2x+1/x-3 nilai dari f-1 (15) adalah….

Jawab
 
g(x)= (2x  +1)/( x- 3)

fog(x)=  5x – 1

f{ (2x +1) /(x – 3)} = 5x – 1

f⁻¹ (5x – 1)  = [ (2x + 1) / (x – 3) ]
5x -1 = 15
5x = 16
x = 16/5

f⁻¹ (15) = [  (2(16/5 )  + 1 ) / (16/5 – 3 ]
f⁻¹ (15) = [ 32/5 + 1 ] / [ 16/5 – 3] = [ 32 + 5 ] / [16 – 15]
f-1 (15)= 37