求证三角函数!help
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求证三角函数!help求证三角函数!help求证三角函数!help1.cos3x=4cosx*cos(60°-x)*cos(60°+x)cos12°*cos24°*cos48°*cos96°=(4co
求证三角函数!help
求证三角函数!help
求证三角函数!help
1.cos3x=4cosx*cos(60°-x)*cos(60°+x)
cos12°*cos24°*cos48°*cos96°
=(4cos12°*cos48°*cos72°)*(4cos36°*cos24°*cos96°)/(16cos72°*cos36°)
=cos36°*cos108°/(16cos72°*cos36°)=-1/16
2.sin2x=2sinx*cosx
cos12°*cos24°*cos48°*cos96°
=sin24°/(2sin12°)*sin48°/(2sin24°)*sin96°/(2sin96°)*sin192°/(2sin96°)
=-1/16
附：cos3x=4cos³x-3cosx sin3x=3sinx-4sin³x
cosx*cosy=1/2*(cos(x+y))*cos(x-y)) sinx*siny=1/2(cos(x-y)-cos(x+y))