Question

已知角α在第四象限内,sin(2α+二分之三派)＝二分之一，sinα＝

Answer 1

问：已知角α在第四象限内,sin(2α+二分之三派)＝二分之一，sinα＝

答：∵sin(3π/2+ a)=-cosasin(2a+3π/2)=1/2∴sin(3π/2+2a)=-cos2a=1/2∴cos2a=-1/2∵cos2a=1-2sin^a, a位于第四象限∴sina=-根号[(1-cos2a)/2]=-2分之根号3

答：∵sin(3π/2+ a)=-cosasin(2a+3π/2)=1/2∴sin(3π/2+2a)=-cos2a=1/2∴cos2a=-1/2∵cos2a=1-2sin^a, a位于第四象限∴sina=-根号[(1-cos2a)/2]=-根号[(1+1/2)/2]=-2分之根号3

答：∵sin(3π/2+ a)=-cosasin(2a+3π/2)=1/2∴sin(3π/2+2a)=-cos2a=1/2∴cos2a=-1/2∵cos2a=1-2sin^2a, a位于第四象限∴sina=-根号[(1-cos2a)/2]=-根号[(1+1/2)/2]=-2分之根号3

答：最后一段是完整的正确答案