apologies in advance, i'm quite new to these forums and don't know how to illustrate my question the proper way. i'll state my steps clearly and what i did in each step in brackets next to the equation.

(Using double angle formula )

(figured out the value of )

(Moved the -1 to the left, making +1)

(Divided both sides by 2)

(Square root of both sides)

seem correct? havn't got the answers in the back of my book. Seems right to me but i have to be sure i can use this method in my test. Would i be able to use this method for Tan, Sin, Cos and their recipricols?