Bài 1:1: \(=\dfrac{20}{15}\cdot\dfrac{x^2}{x}\cdot\dfrac{y^2}{y^7}=\dfrac{\dfrac{4}{3}x}{y^5}\)2: \(=\dfrac{25}{40}\cdot\dfrac{x^4}{x^5}\cdot\dfrac{y^7}{y^4}=\dfrac{5y^3}{8x}\)3: =-45/18*x^7/x^5*y^4/y^8\(=\dfrac{-5x^2}{2y^4}\)4: \(=\dfrac{3\left(x-y\right)^2}{9\left(x-y\right)\left(x+y\right)}=\dfrac{\left(x-y\right)}{3\left(x+y\right)}\)5: \(=\dfrac{5b\left(3a+b\right)}{\left(3a+b\right)\left(3a-b\right)}=\dfrac{5b}{3a-b}\)6: =(a+b)^2/(a+b)=a+b7: =3(x-y)(x+y)/9(x+y)\(=\dfrac{x-y}{3}\)8: =(x-y)(x+y)/a(x-y)=(x+y)/a9: =(m-2)^2/2(m-2)=(m-2)/210: =(x-y)^2/3(x-y)=(x-y)/3Câu trả lời: Bài 1:1: \(=\dfrac{20}{15}\cdot\dfrac{x^2}{x}\cdot\dfrac{y^2}{y^7}=\dfrac{\dfrac{4}{3}x}{y^5}\)2: \(=\dfrac{25}{40}\cdot\dfrac{x^4}{x^5}\cdot\dfrac{y^7}{y^4}=\dfrac{5y^3}{8x}\)3: =-45/18*x^7/x^5*y^4/y^8\(=\dfrac{-5x^2}{2y^4}\)4: \(=\dfrac{3\left(x-y\right)^2}{9\left(x-y\right)\left(x+y\right)}=\dfrac{\left(x-y\right)}{3\left(x+y\right)}\)5: \(=\dfrac{5b\left(3a+b\right)}{\left(3a+b\right)\left(3a-b\right)}=\dfrac{5b}{3a-b}\)6: =(a+b)^2/(a+b)=a+b7: =3(x-y)(x+y)/9(x+y)\(=\dfrac{x-y}{3}\)8: =(x-y)(x+y)/a(x-y)=(x+y)/a9: =(m-2)^2/2(m-2)=(m-2)/210: =(x-y)^2/3(x-y)=(x-y)/3