There are two parts to this proof
Part 1,
Part 2,
Let us compute part 1 first,
The above doesn't need to be proved, it is simple expansion.
Let be the anti-derivative of and let be the anti-derivative of
In other words,
and
Noting that
This is produced by both of the following,
and
Thus,
But I didn't include the constants, here. So what we are left with from the question is
Let be the anti-derivative of
Then,
So,