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Cos2x等于什么??

cos2X=(cosX)^2-(sinX)^2 =2*(cosX)^2-1 =1-2*(sinX)^2

cos2X=(cosX)^2-(sinX)^2 =2*(cosX)^2-1 =1-2*(sinX)^2

cos2X=(cosX)^2-(sinX)^2 =2*(cosX)^2-1 =1-2*(sinX)^2

2cos2X=2(cosX)^2-2(sinX)^2 =4*(cosX)^2-2 =2-4*(sinX)^2

这是一个复合函数的导数,有两层,外层是cos的导数,内层是2x的导数,所以 =-sin2x * (2x)的导数=-2sin2x

原式=1-(1-2sin²x) =2sin²x

cos2x=(1-tan^2x)/(1+tan^2x),你写错了.这公式叫做万能公式.证明:

1+cos2x =1+(2cos²x-1) =2cos²x 这是2倍角公式的余弦公式:cos2x=2cos²x-1

sinxcos2x=1/2(sinxcos2x+cosxsin2x+sinxcos2x-cosxsin2x)=1/2(sin(x+2x)+sin(x-2x))=1/2(sin3x-sinx)

cosx*(2(cosx)^2-1)=2(cosx)^3-cosx

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