Rmd_1, thanks for the advice. For all, the questions are:
1. Find ∫ (0 --> 1/2) dx / (1 - x<sup>2</sup>)<sup>3/2</sup>, where the answer is 1 / √3
2. Find ∫ (tan x --> cot x) dt / (1 + t<sup>2</sup>), for 0 < x < π / 2, where the answer is (π / 2) - 2x
3. Find ∫ x / sqrt(1 + x<sup>2</sup>) dx, where the answer is sqrt(1 + x<sup>2</sup>) + C