please provide steps

7. a. Let D be the domain bounded by the a-axis, the y-axis, and the line a ty 1. Compute Hint: Use the change of variables sea ty and to- 2 - y. which is equivalent to F Landy ,. Note that (r. ") - D if and only if 0 2 s s. land -s 5 1 5 s. b. Use the change of variables to polar coordinates to show that the area of a circle of radius P is 7 1, ie., prove that