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三角函数二倍角推导过程 正弦二倍角推导： sin2A = sin(A+A) = sinAcosA + cosAsinA = 2sinAcosA 余弦二倍角推导： cos2A = cos(A+A) = cosAcosA - sinAsinA = cos^2 A- sin^2 A = 2cos^2 A - 1 =1-2sin^2 A 正切二倍角推导： tan(2a) = tan(a+a) = (tan(a) + tan(a))/(1 - tan(a)*tan(a) ) = 2tanα/[1 -(tanα)^2] (责任编辑：admin) |