Question

tìm x biết :      b)\(\frac{x-1}{7}\)=\(\frac{9}{x+1}\)                     c)\(\frac{x-2}{x-1}\)=\(\frac{x+4}{x+7}\)

Answer 1

b) \(\frac{x-1}{7}=\frac{9}{x+1}\)

\(\Rightarrow\left(x-1\right).\left(x+1\right)=9.7\)

\(\Rightarrow x^2-1=63\)

\(\Rightarrow x^2=63+1\)

\(\Rightarrow x=8\)hoặc \(-8\)

Answer 2

b) ta có : 

\(\left(x-1\right).\left(x+1\right)=7.9\)