Hi guyz! Can u pls help me with this baffling trigo identity? If tan^2 A -2 tan^2 B = 1, show that cos^2 B = 2 cos^2 A.
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$\sec^2{a}-1-2(\sec^2{b}-1)=1$ $\sec^2{a}-2\sec^2{b}=0$ $\dfrac{1}{\cos^2{a}}=\dfrac{2}{\cos^2{b}}$ finish by cross-multiplying ...
Thanx aplenty! Why didn't I think of that?