cos(pai/5)cos((2/5) pai)的

cos(pai/5)cos((2/5) pai)的值是～

1个回答

[2sin(π/5)*cos(π/5)*cos(2π/5)]/2sin(π/5)=sin(2π/5)*cos(2π/5)/2sin(π/5)==[2*sin(2π/5)*cos(2π/5)]/2*2sin(π/5)=sin(4π/5)/4sin(π/5)=1/4

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