It seems easy but I don't know why am I not able to solve it.
friendship is tan 90°.
So I thought: replace every cos^2 with 1 - sin^2 and simplify. (I've left out some simplification steps ... you'll have to put them in yourself.)
Now to use the given equation:
Use this to simplify E by removing the highest power:
Go back to the given equation and use it again to remove the 4th power term:
You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei