大师作文网二倍角的推导有好几条 要过程```````
来源：学生作业帮 编辑：大师作文网作业帮 分类：数学作业 时间：2024/11/11 07:23:58
二倍角的推导
有好几条 要过程```````
有好几条 要过程```````
sin2x=sin(x+x)
=sinxcosx+cosxsinx
=2sinxcosx
cos2x=cos(x+x)
=cosxcosx-sinxsinx
=(cosx)^2-(sinx)^2
=(cosx)^2-[1-(cosx)^2]
=2(cosx)^2 - 1
=[1-(cosx)^2]-(sinx)^2
=1-2(sinx)^2
tan2x=tan(x+x)
tanx + tanx
=----------------
1 - tanxtanx
2tanx
=----------------
1 - (tanx)^2
同理sinx=2sin(x/2)cos(x/2)
cosx=[cos(x/2)]^2-[sin(x/2)]^2
=2[cos(x/2)]^2-1
=1-2[sin(x/2)]^2
2tan(x/2)
tanx=---------------
1-[tan(x/2)]^2
=sinxcosx+cosxsinx
=2sinxcosx
cos2x=cos(x+x)
=cosxcosx-sinxsinx
=(cosx)^2-(sinx)^2
=(cosx)^2-[1-(cosx)^2]
=2(cosx)^2 - 1
=[1-(cosx)^2]-(sinx)^2
=1-2(sinx)^2
tan2x=tan(x+x)
tanx + tanx
=----------------
1 - tanxtanx
2tanx
=----------------
1 - (tanx)^2
同理sinx=2sin(x/2)cos(x/2)
cosx=[cos(x/2)]^2-[sin(x/2)]^2
=2[cos(x/2)]^2-1
=1-2[sin(x/2)]^2
2tan(x/2)
tanx=---------------
1-[tan(x/2)]^2