Please tell me how to solve this problem and let me know what equation u used.

dw 19. Let w = xycosz, where x = to, y = to, and z = arccost. Find dt 20. Find a vector-valued function, using the given parameter, to represent the intersection of the surfaces given below. Surfaces Parameter x2+ y2 = 9. z=x2 x = 3sin(8 7tt)16. Use the given acceleration function and initial conditions to find the position at time t = 3. a(t) =-8i + 4j+ 10k, v(0) = 0, r(0) = 5j 17. Find VA(x, y) for function f(x, y) = 9- - y 9 2 18. Identify the following quadric surface. 5 10 O