Problem 4 Partial derivatives. Consider the function defined by f (t. x, y) = ch() sin(mx) cos(ny) where m and n are two arbitrary parameters. Find all functions h(t) such that f is a solution to the differential equation fi = fix + fvyProblem 3 Limit and Continuity. (i) At what points is f(x, y) continuous? f(x,y) = 13 + 12: (x, y) # (0.0). 1: (r, y) = (0. 0). (ii) Find lim(z.v)-+(0,0) r+12 /x3+ 12+4 -2