Chapter 14.4, Problem 9E

Draw the graph of f and its tangent plane at the given point. (Use your computer algebra system both to compute the partial derivatives and to graph the surface and its tangent plane.) Then zoom in until the surface and the tangent plane become indistinguishable.

$f\left(x,y\right)=\frac{1+{\cos }^2\left(x-y\right)}{1+{\cos }^2\left(x+y\right)}$, $\left(\frac{\pi }{3},\frac{\pi }{6},\frac{7}{4}\right)$