Question

3√2 cos^2(pi/8) - 3√2 sin^2(pi/8)

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Answer 1

$3\sqrt{2}Cos^{2}\frac{\pi }{8}-3\sqrt{2}Sin^{2}\frac{\pi }{8}=3\sqrt{2}(Cos^{2}\frac{\pi }{8}-Sin^{2}\frac{\pi }{8})=3\sqrt{2}Cos(2*\frac{\pi }{8})=3\sqrt{2}Cos\frac{\pi }{4}=3\sqrt{2}*\frac{1}{\sqrt{2} }=3$