Tìm nguyên hàm của hàm số f(x)= 7^x+1 / 8^x. tích phân f(x)dx = 7/ln7/8 .(7/8)^-x +C

A. $\int f\left(x\right)dx=\frac{7}{\ln {\displaystyle \frac{7}{8}}}.{\left(\frac{7}{8}\right)}^{-x}+C$

B. $\int f\left(x\right)dx=\frac{8}{\ln {\displaystyle \frac{7}{8}}}.{\left(\frac{7}{8}\right)}^{-x}+C$

C. $\int f\left(x\right)dx=\frac{7}{\ln {\displaystyle \frac{7}{8}}}.{\left(\frac{7}{8}\right)}^x+C$

D. $\int f\left(x\right)dx=\frac{8}{\ln {\displaystyle \frac{7}{8}}}.{\left(\frac{7}{8}\right)}^x+C$