Question

cos²15°-sin²15° срочно​

Answer 1

Вот как-то так)…………..

Answer 2

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$\boxed {\Big \displaystyle sin^2 \ \frac{x}{2}=\frac{1-cosx}{2} }$

$\displaystyle\bf cos^215^\circ-sin^215^\circ=1-sin^2-sin^215^\circ=1-2sin^215^\circ=1-\frac{2\Big(1-cos30^\circ \Big)}{2} =\\1-1cos^230^\circ=\frac{\sqrt{3}}{2}$