已知θ是第三象限角,丨cosθ丨=m,sin(θ/2)+cos(θ/2)>0,则cos(θ/2)=?A.-根号下(1-m)/2 B.-根号下(1+m)/2 C.+/-根号下(1-m)/2D.根号下(1+m)/2
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![已知θ是第三象限角,丨cosθ丨=m,sin(θ/2)+cos(θ/2)>0,则cos(θ/2)=?A.-根号下(1-m)/2 B.-根号下(1+m)/2 C.+/-根号下(1-m)/2D.根号下(1+m)/2](/uploads/image/z/8612644-4-4.jpg?t=%E5%B7%B2%E7%9F%A5%CE%B8%E6%98%AF%E7%AC%AC%E4%B8%89%E8%B1%A1%E9%99%90%E8%A7%92%2C%E4%B8%A8cos%CE%B8%E4%B8%A8%3Dm%2Csin%28%CE%B8%2F2%29%2Bcos%28%CE%B8%2F2%29%EF%BC%9E0%2C%E5%88%99cos%28%CE%B8%2F2%29%3D%3FA.-%E6%A0%B9%E5%8F%B7%E4%B8%8B%EF%BC%881-m%EF%BC%89%2F2+B.-%E6%A0%B9%E5%8F%B7%E4%B8%8B%EF%BC%881%2Bm%EF%BC%89%2F2+C.%2B%2F-%E6%A0%B9%E5%8F%B7%E4%B8%8B%EF%BC%881-m%EF%BC%89%2F2D.%E6%A0%B9%E5%8F%B7%E4%B8%8B%EF%BC%881%2Bm%EF%BC%89%2F2)
已知θ是第三象限角,丨cosθ丨=m,sin(θ/2)+cos(θ/2)>0,则cos(θ/2)=?A.-根号下(1-m)/2 B.-根号下(1+m)/2 C.+/-根号下(1-m)/2D.根号下(1+m)/2
已知θ是第三象限角,丨cosθ丨=m,sin(θ/2)+cos(θ/2)>0,则cos(θ/2)=?
A.-根号下(1-m)/2 B.-根号下(1+m)/2 C.+/-根号下(1-m)/2
D.根号下(1+m)/2
已知θ是第三象限角,丨cosθ丨=m,sin(θ/2)+cos(θ/2)>0,则cos(θ/2)=?A.-根号下(1-m)/2 B.-根号下(1+m)/2 C.+/-根号下(1-m)/2D.根号下(1+m)/2
θ是第三象限角,
丨cosθ丨=m, cosθ=-m
θ=2kπ+π+a
a ∈(0,π/2)
θ/2= kπ+π/2 +a/2
π/2 +a/2 ∈(π/2, 3π/4)
∵ sin(θ/2)+cos(θ/2)>0,
可以知道 θ/2 ∈ (2kπ-π/4, 2kπ+3π/4)
∴k 是偶数,设k为2n
θ/2= 2nπ+π/2 +a/2
第二象限角 cos(θ/2)小于0
cosθ=-m= 2cos²(θ/2)-1
cos(θ/2)= -√[ (1-m)/2]
已知θ是第三象限角,丨cosθ丨=m,sin(θ/2)+cos(θ/2)>0,则cos(θ/2)=?良驹绝影 ~
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已知θ是第三象限角,│cosθ│=m,且sinθ/2+cosθ/2>0,则cosθ/2=?
已知θ是第三象限角,丨cosθ丨=m,sin(θ/2)+cos(θ/2)>0,则cos(θ/2)=?A.-根号下(1-m)/2 B.-根号下(1+m)/2 C.+/-根号下(1-m)/2D.根号下(1+m)/2
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