im supposed to eliminate A from the pair of equations
x= sin2A
y= sec4A
ive learnt most trig identities i think, up to the double angle identities etc.
ive done several problems like this but here im really stuck
i passed through those already, including the sin2A double angle identity which i already figured might be totally irrelevant to this problem. but where do i go from cos4A? i really didnt need someone to repeat these identities to me. im actually stuck.
Actually, I think you did need the identity being repeated to you. It was being brought to your attention because it is relevant to answering the question. The hope was that you would contemplate how it was linked to the question, see
$\displaystyle x = {\color{red}\sin (2A)}$
$\displaystyle y = \sec (4A) = \frac{1}{\cos (4A)} = \frac{1}{1 - 2 {\color{red}\sin^2 (2A)}}$
and then join the dots ....