Question

найдите значение выражения √2cos^2 3pi/8- √2sin^2 3pi/8

Answer 1

$\sqrt2\, cos^2\frac{3\pi }{8}-\sqrt2\, sin^2\frac{3\pi }{8}=\sqrt2\cdot (cos^2\frac{3\pi }{8}-sin^2\frac{3\pi }{8})=\\\\=\sqrt2\cdot cos\frac{6\pi }{8}=\sqrt2\cdot cos\frac{3\pi}{4}=\sqrt2\cdot (-\frac{\sqrt2}{2})=-1\\\\\\\star \; \; cos^2\alpha -sin^2\alpha =cos\, 2\alpha \; \; \star$

Answer 2

----------------------