((cos^2 3pi/8)-(cos^2 pi/8))* cos39pi/4

Question

((cos^2 3pi/8)-(cos^2 pi/8))* cos39pi/4

Comments

((1+cos (3pi/4)/2-(1+cos (pi/4))/2)*cos (39pi/4)=

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=1/2 (cos (3pi/4)-cos (pi/4))*cos (10pi-pi/4)=

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1/2 (-cos (pi/4)-cos (pi/4))*cos (pi/4)=-cos^2 (pi/4)=-(1/sqrt (2))^2=-1/2

Answer 1

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