Question 5.(10 points) Assume that z=f(x,y) is a differentiable function defined implicitly by the equationzcos(xy)=xsin(yz)and let f(1,2)=2.(a)(5 pts) Find fx(1,2) and fy(1,2).(b)(5 pts) Find the maximum directional derivative of f at point (1,2) and the unit vector pointing in the direction along which z=f(x,y) increases fastest at the point (1,2).