Answer: Absolutely Never. No. He didn't do it correctly. Don't you do it.
I have never seen that error on Brainly before, although while I was teaching, I saw it enough times that I could always bet my math classes that I would see that error 100 times by the end of term. I always promised a case of beer for their grad (which would have given them 1 beer each). I never had to pay. They always made the error 100 times as a class.
Micah CANNOT cancel across a plus sign when going from the numerator to the denominator. You have to be able to take an x^2 out of every term or no term. Micah is totally wrong. Don't, whatever you do, follow his example.
Here is the only condition which will permit you that kind of cancellation.
Now Micah can cancel out the x^2. That is the only condition that will work.