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Squaring on both sides $$\cos^2 x + \cos^2 y + 2\cos x \cos y=1$$ I know w don’t generally square while finding general solutions, but I couldn’t see any other way $$\cos^2 x +\cos^2 y=1/2$$ I couldn’t solve further. How should I proceed?

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    $\begingroup$ Finding two numbers given product and sum is equivalent to solving a quadratic equation... $\endgroup$ – dfnu Nov 20 '19 at 13:38
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    $\begingroup$ Yeah, that works, didn’t think like that. Thanks! $\endgroup$ – Aditya Nov 20 '19 at 13:53
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Hint.

Can you solve for $a, b$

$$ \cases{a+b=1\\ a b = \frac 14} $$ ?

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