sin(π/4 - x)=sin[π/2 - (π/4 + x)]=cos(π/4 + x)=m
sin(π/4 + x)=±√1 - cos²(π/4 + x)=±√1 - m²
∵x是第一象限角
∴sin(π/4 + x)=√1 - m²
sin(5π/4+x)=sin(π + π/4 + x)=-sin(π/4 + x)=-√1 - m²
已知sin(π/4-x)=m x是第一象限角 求sin(5π/4+x)的值
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