Question

вообще не понимаю, буду очень благодарна за

Answer 1

$1)\ \ \dfrac{2\, tg75^\circ }{1-tg^275^\circ }=tg(2\cdot 75^\circ )=tg150^\circ =tg(180^\circ -30^\circ )=-tg30^\circ =-\dfrac{\sqrt3}{3}\\\\\\2)\ \ 2\, sin\dfrac{3\pi}{8}\cdot cos\dfrac{3\pi}{8}=sin\dfrac{6\pi}{8}=sin\dfrac{3\pi}{4}=sin\Big(\pi -\dfrac{\pi}{4}\Big)=sin\dfrac{\pi}{4}=\dfrac{\sqrt2}{2}$

$3)\ \ 1-2cos^2\dfrac{\pi}{12}=\Big(sin^2\dfrac{\pi}{12}+cos^2\dfrac{\pi}{12}\Big)-2cos^2\dfrac{\pi }{12}=sin^2\dfrac{\pi}{12}-cos^2\dfrac{\pi}{12}=\\\\\\=-\Big(cos^2\dfrac{\pi}{12}-sin^2\dfrac{\pi}{12}\Big)=-cos\Big(2\cdot \dfrac{\pi}{12}\Big)=-cos\dfrac{\pi}{6}=-\dfrac{\sqrt3}{2}$