作业帮sin2x/(sinx+cosx-1)(sinx-cosx+1)答案确定正确
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sin2x/(sinx+cosx-1)(sinx-cosx+1)答案确定正确
sin2x/(sinx+cosx-1)(sinx-cosx+1)
答案确定正确
sin2x/(sinx+cosx-1)(sinx-cosx+1)答案确定正确
(sinx+cosx-1)(sinx-cosx+1)/sin2x =[sinx+(cosx-1)][sinx-(cosx-1)]/sin2x =[(sinx)^2-(cosx-1)^2]/sin2x =[(sinx)^2-(cosx)^2-1+2cosx]/sin2x ={(sinx)^2-(cosx)^2-[(sinx)^2+(cosx)^2]+2cosx}/sin2x =[2cosx-2(cosx)^2]/sin2x =2cosx(1-cosx)/2sinxcosx =(1-cosx)/sinx =tanx/2 得证