here's the problem.
i don't know how to solve this , can you help me? thanks.
I'll show you how to do the second question, but if I shall help you I must know what exactly is confusing you.
Ooooh, I finally found your question in the quoted calculations.
If you have then you can simplify
Apply similar transformations with all summands in the numerator and you'll get the next line of my calculations.
And now the 2nd question:
Honestly, I don't know what you did and why?
All my calculations were necessary to get a rational denominator. Thus I multiplied numerator and denominator by which I marked in red. That means I didn't change the value of the quotient.
The product of the numerator and is
which I simplified to
That's all.