Question

1a,Tìm x, biết:\(\frac{x}{6}+\frac{x}{4}=\frac{5}{7}\)

b,Cho M=\(x^2y-xy^2-5x+5y-12\)Tính M khi xy=5

Answer 1

a ) \(\frac{x}{6}+\frac{x}{4}=\frac{5}{7}\)

\(\Leftrightarrow x\left(\frac{1}{6}+\frac{1}{4}\right)=\frac{5}{7}\)

\(\Leftrightarrow\frac{5}{12}x=\frac{5}{7}\)

\(\Rightarrow x=\frac{5}{7}:\frac{5}{12}\)

\(\Rightarrow x=\frac{12}{7}\)

b ) Nếu \(xy=5\) thì :

\(M=x^2y-xy^2-xy.x+xy.y-12\)

\(=x^2y-xy^2-x^2y+xy^2-12\)

\(=\left(xy^2-x^2y\right)+\left(-xy^2+xy^2\right)-12\)

\(=-12\)