In each of Problems 18 through 22, (a) sketch the domain F over which the integration is performed; (b) write the equivalent iterated integral in the reverse order; (c) evaluate the integral obtained in (b). Describe Fusing set notation (in both orders). 18. ,2 dy dx 19. xydydx V4-X 20. (a' - 2)312 dy dx 21 1 + x- dx dy o 22. V 1 + y' dy dx X