若(sinθ+cosθ)/(sinθ-cosθ)=2,那么sin(θ-5π)*sin(3π/2-θ)的值是A.3/4 B.±3/10 C.3/10 D.-3/10我算出来是9/10 和答案都不一样、请问应该选什么、为什么、
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![若(sinθ+cosθ)/(sinθ-cosθ)=2,那么sin(θ-5π)*sin(3π/2-θ)的值是A.3/4 B.±3/10 C.3/10 D.-3/10我算出来是9/10 和答案都不一样、请问应该选什么、为什么、](/uploads/image/z/5222585-65-5.jpg?t=%E8%8B%A5%28sin%CE%B8%2Bcos%CE%B8%29%2F%28sin%CE%B8-cos%CE%B8%29%3D2%2C%E9%82%A3%E4%B9%88sin%28%CE%B8-5%CF%80%29%2Asin%283%CF%80%2F2-%CE%B8%29%E7%9A%84%E5%80%BC%E6%98%AFA.3%2F4+B.%C2%B13%2F10+C.3%2F10+D.-3%2F10%E6%88%91%E7%AE%97%E5%87%BA%E6%9D%A5%E6%98%AF9%2F10+%E5%92%8C%E7%AD%94%E6%A1%88%E9%83%BD%E4%B8%8D%E4%B8%80%E6%A0%B7%E3%80%81%E8%AF%B7%E9%97%AE%E5%BA%94%E8%AF%A5%E9%80%89%E4%BB%80%E4%B9%88%E3%80%81%E4%B8%BA%E4%BB%80%E4%B9%88%E3%80%81)
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若(sinθ+cosθ)/(sinθ-cosθ)=2,那么sin(θ-5π)*sin(3π/2-θ)的值是A.3/4 B.±3/10 C.3/10 D.-3/10我算出来是9/10 和答案都不一样、请问应该选什么、为什么、
若(sinθ+cosθ)/(sinθ-cosθ)=2,那么sin(θ-5π)*sin(3π/2-θ)的值是
A.3/4 B.±3/10 C.3/10 D.-3/10
我算出来是9/10 和答案都不一样、请问应该选什么、为什么、
若(sinθ+cosθ)/(sinθ-cosθ)=2,那么sin(θ-5π)*sin(3π/2-θ)的值是A.3/4 B.±3/10 C.3/10 D.-3/10我算出来是9/10 和答案都不一样、请问应该选什么、为什么、
(sinθ+cosθ)/(sinθ-cosθ)=2
2sinθ-2cosθ=sinθ+cosθ
sinθ=3cosθ
sin²θ+cos²θ=1
9cos²θ+cos²θ=1
cos²θ=1/10
sin(θ-5π)*sin(3π/2-θ)
=sin(θ+6π-5π)*sin(3π/2-θ-2π)
=sin(θ+π)*sin(-θ-π/2)
=(-sinθ)*[-sin(θ+π/2)]
=sinθ*sin(θ+π/2)
=sinθ*cosθ
=3cos²θ
=3/10
应该选C
由题设可得到tanθ=3
sin(θ-5π)*sin(3π/2-θ)=(1/2)sin2θ
套用万能公式得3/10
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