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答: 解:cos54°=sin36° ==>cos(3·18°)=sin(2·18°) ==>4...
答: 解法1.令x = 18° ∴cos3x = sin2x ∴4(cosx)^3 - 3cos...
答: 解: sin90=sin5*18=sin(3*18+2*18) =sin3*18c...
答: sin18度-cos36度 =(√5-1)/4-(√5+1)/4=-1/2; 注:sin1...
答: (sin18+sin54)^2 =0.5(1-cos36)+0.5(1-cos108)+2...
答: [(√3tan48-1)/2sec48]+2(sin18)^2=? =[(√3sin48-...
答: 求sin18度与cos36度. 详见附件
答: 利用三倍角公式: sin3t=3sint-4(sint)^3 设sin20°=x,则由上述...
答: sin2A=2sinAcosA--->cosA=sin2A/(2sinA) sin18+2...
答: 由sin36°=cos54°和倍角公式,得 2sin18°cos18°=4(cos18°)...
答: cos3A=cos(2A+A)=cos2AcosA-sin2AsinA =[1-2(sin...
答: cos36*sin18=cos36*sin18*cos18/cos18=1/2sin36c...
答: 18度=36/2度=90/5度,从某个角度来说,也是特殊角,所以,我在中学时就计算过, S...
答: cosA=(b^2+c^2-a^2)/2bc (就是余(弓玄)定理) s...
答: cos18度*sin18度*cos36度/cos18度 用二倍角公式,得cos18度*si...
答: 约等于0.316