Jika $f(x)=\frac{x}{x+1}$ dan $g(x)=f(x+1), maka $(g o f)(x)=$ ...
A. $\frac{3x+3}{2x-1}$
B. $\frac{2x-1}{3x+2}$
C. $\frac{2x+1}{3x+2}$
D. $\frac{3x+3}{2x+1}$
E. $\frac{3x-3}{2x+1}$
Jawab;
$g(x)=f(x+1)=\frac{x+1}{(x+1)+1}$
$g(x)=\frac{x+1}{x+2}$
$(g o f)(x)=g(f(x))=\frac{\frac{x}{x+1} +1}{\frac{x}{x+1}+2}$
$=\frac{\frac{x}{x+1}+\frac{1\times (x+1)}{x+1}}{\frac{x}{x+1}\frac{2\times (x+1)}{x+1}}$
$=\frac{\frac{x+x+1}{x+1}}{\frac{x+2x+2}{x+1}}$
$=\frac{\frac{2x+1}{x+1}}{\frac{3x+2}{x+1}}$
$=\frac{2x+1}{3x+2}$
Sumber Soal; Mandiri Matematika Jilid 1 untuk SMA/MA Kelas X Kelompok Wajib, Halaman 93 No. 81
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