a/
\(\left(5xy^2-11x^3y+6x^2y^2\right)\div x^2y\)
\(=xy\left(5y-11x^2+6xy\right)\div x^2y\)
\(=\left(5y-11x^2+6xy\right)\div x\)
\(=\frac{5y}{x}-\frac{11x^2}{x}+\frac{6xy}{x}\)
\(=\frac{5y}{x}-11x+6y\)
b/ \(\left[\left(x+y\right)^5-2\left(x+y\right)^4+3\left(x+y\right)^3\right]\div\left[-5\left(x+y\right)^3\right]\)
\(=\left(x+y\right)^3\left[\left(x+y\right)^2-2\left(x+y\right)+3\right]\div\left[-5\left(x+y\right)^3\right]\)
\(=\frac{\left(x+y\right)^2-2\left(x+y\right)+3}{-5}\)