已知θ∈(5π/2,3π),且sinθ=24/25,则cos(θ/2)等于?
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已知θ∈(5π/2,3π),且sinθ=24/25,则cos(θ/2)等于?
![已知θ∈(5π/2,3π),且sinθ=24/25,则cos(θ/2)等于?](/uploads/image/z/8606608-16-8.jpg?t=%E5%B7%B2%E7%9F%A5%CE%B8%E2%88%88%285%CF%80%2F2%2C3%CF%80%29%2C%E4%B8%94sin%CE%B8%3D24%2F25%2C%E5%88%99cos%28%CE%B8%2F2%29%E7%AD%89%E4%BA%8E%3F)
θ∈(5π/2,3π),第二象限
sinθ=24/25,cosθ=-7/25
θ∈(5π/2,3π),θ/2∈(5π/4,3π/2),第四象限 cos(θ/2)>0
cosθ=2cos^2(θ/2)-1
2cos^2(θ/2)=18/25
cos^2(θ/2)=9/25 cos(θ/2)=3/5
sinθ=24/25,cosθ=-7/25
θ∈(5π/2,3π),θ/2∈(5π/4,3π/2),第四象限 cos(θ/2)>0
cosθ=2cos^2(θ/2)-1
2cos^2(θ/2)=18/25
cos^2(θ/2)=9/25 cos(θ/2)=3/5
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