若(sina+cosa)/(sina -cosa)=2,则 sin(a-5π)*(乘) sin(3π/2 - a)等于?....帮帮~2

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若(sina+cosa)/(sina-cosa)=2,则sin(a-5π)*(乘)sin(3π/2-a)等于?....帮帮~2若(sina+cosa)/(sina-cosa)=2,则sin(a-5π)

若(sina+cosa)/(sina -cosa)=2,则 sin(a-5π)*(乘) sin(3π/2 - a)等于?....帮帮~2
若(sina+cosa)/(sina -cosa)=2,则 sin(a-5π)*(乘) sin(3π/2 - a)等于?
....帮帮~2

若(sina+cosa)/(sina -cosa)=2,则 sin(a-5π)*(乘) sin(3π/2 - a)等于?....帮帮~2
sina+cosa=2sina-2cosa
sina=3cosa
代入恒等式sin²a+cos²a=1
cos²a=1/10
原式=sin(a-π)(-cosa)
=-sina(-cosa)
=sinacosa
=3cosacosa
=3cos²a
=3/10

sin0=0
sinπ/6=0.5
sinπ/4=0.7071=二分之根号2
sinπ/3=0.8660=二分之根号3
sinπ/2=1
cos0=1
cosπ/6=0.866025404=二分之根号3
cosπ/40.707106781=二分之根号2
cosπ/3=0.5
cosπ/2=0