Question

giúp ạ~

Answer 1

Ta có:

\(x-y=9\)

\(\Rightarrow x=y+9\)

Thay \(x=y+9\) vào \(B\) ta được:

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

\(\dfrac{7x+9}{8x-y}=\dfrac{7\left(y+9\right)+9}{8\left(y+9\right)-y}=\dfrac{7y+63+9}{8y+72-y}=\dfrac{7y+72}{7y+72}=1\left(2\right)\)

Từ \(\left(1\right)\) và \(\left(2\right)\)

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

Vậy \(B=2\)

Answer 2

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

Answer 3

Ta có:x-y=9

\(\Rightarrow x=9+y\)

Thay vào BT............

\(\Rightarrow B=2\)

bn tự làm phần.......nhé!!!