Question

giải giúp ạ

Answer 1

Ta có:

\(x-y=9\Leftrightarrow x=y+9\)

Thay \(x=y+9\) vào biểu thức ta có:

\(\dfrac{7x-9}{6x+y}=\dfrac{7\left(y+9\right)-9}{6\left(y+9\right)+y}=\dfrac{7y+63-9}{6y+54+y}=\dfrac{7y+54}{7y+54}=1\)

\(\dfrac{7x+9}{8x-y}=\dfrac{7\left(y+9\right)+9}{8\left(y-9\right)-y}=\dfrac{7y+63+9}{8y+72-y}=\dfrac{7y+72}{7y+72}=1\)

\(\Rightarrow B=\dfrac{7x-9}{6x+y}+\dfrac{7x+9}{8x-y}=1+1=2\)

Vậy \(B=2\)