Question

Cho x+y=10.tim x va y biet: x-3/y+7=3/4

Answer 1

Ta có:

\(\text{x + y = 10 }\)(1)

\(\frac{x-3}{y+7}=\frac{3}{4}\)(2)

Từ (2) suy ra: \(4\left(x-3\right)=3\left(y+7\right)\)

=> \(4x-12=3y+21\)

=> \(4x=3y+21+12\)

=> \(4x=3y+33\)

=> \(4x-3y=33\)(3)

Lấy (3) - 4.(1), vế theo vế, ta có:

\(4x-3y-4\left(x+y\right)=33-4.10\)

=> \(4x-3y-4x-4y=33-40\)

=> \(\left(4x-4x\right)+\left(-3y-4y\right)=-7\)

=>  \(-7y=-7\)

=> \(y=1\)

Thế y = 1 vào (1), ta có:

\(x+1=10\)

=> \(x=9\)