5:
a: \(\dfrac{x^3+x^2}{\left(x-1\right)\left(x+1\right)}=\dfrac{x^2\left(x+1\right)}{\left(x-1\right)\left(x+1\right)}=\dfrac{x^2}{x-1}\)
b: \(\dfrac{5\left(x+y\right)}{2}=\dfrac{5\left(x+y\right)\left(x-y\right)}{2\left(x-y\right)}=\dfrac{5x^2-5y^2}{2x-2y}\)