cos^2 80°+sin^2 50°-sin190°cos320°
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cos^2 80°+sin^2 50°-sin190°cos320°
要求值.
要求值.
![cos^2 80°+sin^2 50°-sin190°cos320°](/uploads/image/z/19661092-52-2.jpg?t=cos%5E2+80%C2%B0%2Bsin%5E2+50%C2%B0-sin190%C2%B0cos320%C2%B0)
sin^2 80 + sin^2 40 - cos50cos10
=cos^2 10 + sin^2 40 - cos50cos10
=(1/2)[(1+cos20)+(1-cos80)-(cos60+cos40)]
=(1/2)[3/2+cos20-(cos80+cos40)]
=(1/2)[3/2+cos20-2cos60cos20]
=3/4
=cos^2 10 + sin^2 40 - cos50cos10
=(1/2)[(1+cos20)+(1-cos80)-(cos60+cos40)]
=(1/2)[3/2+cos20-(cos80+cos40)]
=(1/2)[3/2+cos20-2cos60cos20]
=3/4
sin^2 80°等于 cos^2 10°?
(cos^2 10°-cos^2 80°)+sin^2 20°
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