Question

3√2 cos^2(pi/8) - 3√2 sin^2(pi/8)

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Answer 1

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