5A:
a: \(A=\dfrac{12\left(2x+3y\right)^3-18\left(2x+3y\right)^2}{-6x-9y}\)
\(=\dfrac{-12\left(2x+3y\right)^3+18\left(2x+3y\right)^2}{6x+9y}\)
\(=\dfrac{-12\left(2x+3y\right)^3}{3\left(2x+3y\right)}+\dfrac{18\left(2x+3y\right)^2}{3\left(2x+3y\right)}\)
\(=-4\left(2x+3y\right)^2+6\left(2x+3y\right)\)
Khi x=3/2 và y=1 thì \(A=-4\left(2\cdot\dfrac{3}{2}+3\right)^2+6\left(2\cdot\dfrac{3}{2}+3\right)\)
\(=-4\cdot36+6\cdot6=-3\cdot36=-108\)
b: \(B=\dfrac{\left(2x-y\right)^4+8\left(y-2x\right)^2-2x+y}{2y-4x}\)
\(=\dfrac{-\left(2x-y\right)^4-8\left(2x-y\right)^2+\left(2x-y\right)}{4x-2y}\)
\(=\dfrac{-\left(2x-y\right)^4-8\left(2x-y\right)^2+\left(2x-y\right)}{2\left(2x-y\right)}\)
\(=\dfrac{-\left(2x-y\right)^3-8\left(2x-y\right)+1}{2}\)
Khi x=1 và y=-2 thì \(B=\dfrac{-\left(2+2\right)^3-8\left(2+2\right)+1}{2}\)
\(=\dfrac{-64-32+1}{2}=\dfrac{-95}{2}\)
