# C3 identity issue!

• Dec 11th 2012, 01:36 PM
DonGorgon
C3 identity issue!
Can someone please direct me in the correct identities to use here, really stuck!

given that 5sec^2x + 3tan^2x =9, find the possible values of sin x.

Thanks!
• Dec 11th 2012, 02:07 PM
MarkFL
Re: C3 identity issue!
Multiply through by $\cos^2(x)$ then apply the Pythagorean identity to get a quadratic in $\sin^2(x)$.
• Dec 11th 2012, 02:12 PM
OllieC
Re: C3 identity issue!
Knowing that: tan^2x + 1 = sec^2x, sec^2x = 1/cos^2x and also sin^2x + cos^2x = 1, is what is required to answer this question.
More specifically begin by getting everything in terms of sin x and cos x and hopefully it will become much easier to manipulate.
• Dec 24th 2012, 02:52 AM
ibdutt
Re: C3 identity issue!