Steps to get the answer 1. Analyse the standard formula well. 2. write down the value of angle ,which is with variable X or any other variable if mentioned . 3. Here if you observe you will get "a & b " are the angles with X ( SEE FORMULA ) 4. Now take square of "a & b" & divide both of them like ( a^2 - b^2) / 2 & so the result . Any queries from this please mail us or you can comment your doubt in the comment box Thank you !!!