I guess this is the exercice:
?
Write:
Can you now finish it? ...
You made a mistake in your derivative, but in your first post it was correct so I guess you didn't see it:
So you get indeed:
Now, you can wright, like I said before:
So you get:
Now if you multiply the left fraction with in the numerator and denominator you'll get the same denominator as the right fraction, so: