$2.)$ Compute the following derivatives I partial deninatives

a$)\frac{\text{d}\text{e}\text{l}\text{f}}{\text{d}\text{e}\text{l}\text{x}}$ of $f(x)=x^2{e}^{cosx}$

b$.)f(x,y)=sin(y-x{)}^{3}cos{e}^{x+y}$