not sure to put this in pre calculus or calculus, sorry if mistaken

Find the following limit.

Given that where ,

find

the answer given is:

since

since

therefore, when

therefore

i don't understand how and is found.

what i find instead is and

using that, i also find

but please help explain the steps, as the steps in the answers are pretty different from those that i use, im afraid that i've mistaken