sin(a-b)=5/13,sin(a+b)= -5/13且a-b∈(π/2,π),a+b∈(3π/2,2π),求cos2b的值
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![sin(a-b)=5/13,sin(a+b)= -5/13且a-b∈(π/2,π),a+b∈(3π/2,2π),求cos2b的值](/uploads/image/z/14764609-1-9.jpg?t=sin%28a-b%29%3D5%2F13%2Csin%28a%2Bb%29%3D+-5%2F13%E4%B8%94a-b%E2%88%88%EF%BC%88%CF%80%2F2%2C%CF%80%EF%BC%89%2Ca%2Bb%E2%88%88%EF%BC%883%CF%80%2F2%2C2%CF%80%EF%BC%89%2C%E6%B1%82cos2b%E7%9A%84%E5%80%BC)
sin(a-b)=5/13,sin(a+b)= -5/13且a-b∈(π/2,π),a+b∈(3π/2,2π),求cos2b的值
sin(a-b)=5/13,sin(a+b)= -5/13且a-b∈(π/2,π),a+b∈(3π/2,2π),求cos2b的值
sin(a-b)=5/13,sin(a+b)= -5/13且a-b∈(π/2,π),a+b∈(3π/2,2π),求cos2b的值
cos2b=cos[(a+b)-(a-b)]=cos(a+b)cos(a-b)+sin(a+b)sin(a-b)
cos(a-b)=-12/13,cos(a+b)=12/13代入求值即可.
sin(a+b)cosa-cos(a+b)sina=5/13 则sin(π-B)=?
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