Question: Given \(f\left( x,y,z \right)=\sqrt{x+yz},\,\,P\left( 1,3,1 \right),\,\,\,u=\left( \frac{1}{\sqrt{3}},\frac{1}{\sqrt{3}},\frac{1}{\sqrt{3}} \right)\)

(a) Find the gradient of f. (b) Evaluate the gradient at the point P. (c) Find the rate of change of f at P in the direction of u.