8. Find the first partial derivatives of the function f(x,y) Then find the slopes of the tangent planes to the function in the x-direction and the y-direction at the point (1,0). my 9. Find the critical points of the function. Then use the second derivative test to classify the nature of each point, if possible. Finally, determine the relative extrema of the function (if any). f(x,y) = 2 + xy 10. Find the volume of the solid bounded above by the surface z = f(x, y) and below by the plane region R. f(x,y) xe-y? ; R is the region bounded by x = 0, x = v), and y = 4. 11. A forest ranger views a tree that is 400 feet away with a viewing angle of 15º. How tall is the tree to the nearest foot?