Question

Cos^2-sin^2=2cos^2-1

Answer 1

$cos {}^{2} - sin {}^{2} = 2cos {}^{2} - 1 \\ \\ = > lhs = cos {}^{2} - sin {}^{2} \\ \\ = cos {}^{2} - (1 - cos {}^{2} ) \\ \\ = cos {}^{2} - 1 + cos {}^{2} \\ \\ = 2cos {}^{2} - 1 = rhs$

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