sin（π/10）cos（π/5）
=cos(π/10)sin(π/10)cos(π/5)/cos(π/10)
=sin(π/5)cos(π/5)/[2cos(π/10)]
=sin(2π/5)/[4cos(π/10)]
=1/4.
求值：sinπ/10cosπ/5
2个回答
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