求证:(sin2x)除以(sinx+cosx-1)(sinx-cosx+1)等于cotx/2

来源:学生作业帮助网 编辑:六六作业网 时间:2024/12/18 23:46:30
求证:(sin2x)除以(sinx+cosx-1)(sinx-cosx+1)等于cotx/2求证:(sin2x)除以(sinx+cosx-1)(sinx-cosx+1)等于cotx/2求证:(sin2

求证:(sin2x)除以(sinx+cosx-1)(sinx-cosx+1)等于cotx/2
求证:(sin2x)除以(sinx+cosx-1)(sinx-cosx+1)等于cotx/2

求证:(sin2x)除以(sinx+cosx-1)(sinx-cosx+1)等于cotx/2
等式左边=2sinxcosx/[sinx+(cosx-1)][sinx-(cosx-1)]=2sinxcosx/[sin^2x-(cosx-1)^2]=2sinxcosx/(sin^2x-cos^2x+2cosx-1)=2sinxcosx/(2cosx-2cos^2x)=sinx/(1-cosx)=2sin(x/2)cos(x/2)/[1-2cos^2(x/2)+1]=sin(x/2)cos(x/2)/[1-cos^2(x/2)]=sin(x/2)cos(x/2)/sin^2(x/2)=cot(x/2)
过程尽量给你写的很详细了,你要是变角公式很熟练的话,中间很多步可以省略直接得出答案哈