Suppose $\displaystyle f(x,y) = \sqrt{\tan\!\left(x\right)+y}$ and $\boldsymbol{u}$ is the unit vector in the direction of $\left<-2,2\right>$. Then,

(a) $\nabla f (x,y) =$

(b) $\nabla f (-0.9,8) =$

(c) $f_{\boldsymbol{u}} \, (-0.9,8) = D_{\boldsymbol{u}} \, f(-0.9,8) =$