numbers 17 and 19 for section 10.1

10.1.2 In Problems 17-22 find the range of each function f(x, y), when defined on the specified domain D. 17. f(x, y) = x + y; D= ((x,y) :0's9) 19. f(x, y) = In(y -x); D = [(x, y) : 0x) 20. f(x, y) = expl-(x +)]; D = [(x.y) : -1