Partial derivates 3. Determine the first and second order derivatives of the following exercises a) f(x,y) = 8x2 -16y3 b) f(x, y) = 18x2 + 7xy + 6y2 4. Determine only the first-order derivatives of the following exercises a) f(x, y) = 5x2 + xy + 20y3 b) f(x,y) = e5x2-2yz c) f(x, y) =2x2 - 5x3y2 d) u(x, y, z) = x3y2 + y3z2+ 23x2 5. be f(x, y) = -2x2 - 2xy - 2yz + 36x +42y -158, calculate f (0, 1) y f(2,3) 6. The function defined by f (x,y) = -2x2 - 2xy - 2y2 + 36x + 42y - 158 for all (x, y) has a maximum. Find it. (Hint: to find the maximum, you will have to derivate the function partially respect to x and respect to y, and in both cases set equal to zero and solve for each variable.)