Bài 5:
a: \(2xy\cdot\dfrac{4}{5}x^2y^3\cdot10xyz\)
\(=\left(2\cdot\dfrac{4}{5}\cdot10\right)\cdot\left(x\cdot x^2\cdot x\right)\cdot\left(y\cdot y^3\cdot y\right)\cdot z\)
\(=16x^4y^5z\)
b: \(-10y^2\cdot\left(2xy\right)^3\cdot\left(-x\right)^2\)
\(=-10y^2\cdot8x^3y^3\cdot x^2\)
\(=-80x^5y^5\)
Bài 6:
a: \(A=\left(\dfrac{2}{3}x^2y^2\right)\cdot\left(-\dfrac{6}{5}x^4y^3\right)\)
\(=\dfrac{2}{3}\cdot\dfrac{-6}{5}\cdot x^2y^2\cdot x^4y^3\)
\(=-\dfrac{12}{15}\cdot x^2\cdot x^4\cdot y^2\cdot y^3\)
\(=-\dfrac{4}{5}x^6y^5\)
bậc là 6+5=11
b: Thay x=-1;y=-2 vào A, ta được:
\(A=-\dfrac{4}{5}\cdot\left(-1\right)^6\cdot\left(-2\right)^5\)
\(=-\dfrac{4}{5}\cdot1\cdot\left(-32\right)=\dfrac{128}{5}\)
Bài 7:
a: \(-\dfrac{1}{2}x^2y+2x^2y=x^2y\left(-\dfrac{1}{2}+2\right)=\dfrac{3}{2}x^2y\)
b: \(2x^3y-\dfrac{1}{4}x^3y=x^3y\left(2-\dfrac{1}{4}\right)=\dfrac{7}{4}x^3y\)
