I started with the left hand side :
Then i bring out the common factor .
I tried the half angle formula ..
but to no avail .
Hello thereddevilsThanks for showing us your working. But I think there must be something wrong with the question. For any angle , the cosines of and are all positive. So the result can't possibly equal , can it?
When you've got as far as , did you think about using the half-angle formula using ? Then
So ?
Grandad