Problems of advanced mathematics in college liberal arts. How did the first step change to the second step? Find the detailed step answer, the more detailed, the better. Background: After learning the first volume of Advanced Mathematics, This is to regard A 2-R 2 as a whole, which is equivalent to the integral of power function. If the integral limit you write is from 0 to acosθ, the result is as follows.

If the integral limit is from a to acosθ, you can get the result you wrote.