Question

tìm x biết\(\frac{x+7}{-20}=-\frac{5}{x+7}\)  (x khác -7)

 

Answer 1

x+7 / -20 = -5/ x+7

(x+7)(x+7) = -20 .(-5)

(x+7)²= 100

=> ( x+7)²= 10²

=> x+7= 10

x= 10-7

x= 3

Vậy.....

Answer 2

\(\frac{x+7}{-20}=\frac{-5}{x+7}\left(x\ne7\right)\)

<=> (x+7)²=100

<=> \(\orbr{\begin{cases}x+7=10\\x+7=-10\end{cases}\Leftrightarrow\orbr{\begin{cases}x=3\\x=-17\end{cases}}}\)

Answer 3

suy ra (x+7)² = 100=10²

suy ra \(\orbr{\begin{cases}x+7=10\\x+7=-10\end{cases}\Rightarrow\orbr{\begin{cases}x=3\\x=-17\end{cases}}}\)