This is accomplished by doing a "u" substitution. You can see that, because the derivative of what's inside the complex function, x3, is 3x2 and that is what is on top.
So let u = 1 - x3 then du/dx = -3x2 or dx = du/-3z2
The integral becomes:
-∫u-1/2du = -2u1/2 = -2(1 - x3)1/2 + C (answer 4)