Find tanØ if 9sin^2Ø - cos^2Ø =7 I have divided through with cos^2Ø Giving me: 9tan^2Ø - 1 = 7sec^2Ø But I am unsure on how to proceed from there. The books answer gives it as: tanØ = ±2
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$\sec^2(\theta) = 1 + \tan^2(\theta)$ make that substitution and then let $u=\tan(\theta)$ solve the resulting quadratic in $u$ and substitute $\tan(\theta)$ back in.