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来源：学生作业帮助网 编辑：六六作业网 时间：2024/07/31 00:00:32
已知0已知0已知0[cos(β-π/4)]^2=[cosβcos(π/4)+sinβsin(π/4)]^2=[(cosβ)^2+(sinβ)^2]*[cos(π/4)]^2+2*cosβ*sinβ*c
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[cos(β-π/4)]^2=[cosβcos(π/4)+sinβsin(π/4)]^2
=[(cosβ)^2+(sinβ)^2]*[cos(π/4)]^2+2*cosβ*sinβ*cos(π/4)*sin(π/4)
=1/2+1/2*sin2β
=1/9
故 sin2β=-7/9
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