等差：Sn=n(a1+an)/2,Sn=na1+n(n-1)d/2
等比：Sn=a1(1-q^n)/(1-q),Sn=(a1-anq)/(1-q)注意q不=1
三角：
1.基本關(guān)系：(sinx)^2+(cosx)^2=1,tanx=sinx/cosx,secx=1/cosx,cscx=1/sinx,(secx)^2=1+(tanx)^2,(cscx)^2=1+(cotx)^2
2.二倍交公式：sin2x=2sinx*cosx,變形：sinx*cosx=sin2x/2
1+sinx=(sin(x/2))^2+(cos(x/2))^2+2sin(x/2)cos(x/2)=[sin(x/2)+sin(x/2)]^2
1-sinx=(sin(x/2))^2+(cos(x/2))^2-2sin(x/2)cos(x/2)=[sin(x/2)-sin(x/2)]^2
cos2x=(cosx)^2-(sinx)^2
=2(cosx)^2-1,變形：(cosx)^2=(1+cos2x)/2
=1-2(sinx)^2,變形：(sinx)^2=(1-cos2x)/2
tan2x=2tanx/(1-(tanx)^2)
3.兩角和與差公式：sin(x+y)=sinxcosy+sinycosx,sin(x-y)=sinxcosy-sinycosx
cos(x+y)=cosxcosy-sinxsiny,cos(x-y)=cosxcosy+sinxsiny
tan(x+y)=(tanx+tany)/(1-tanxtany),變形：tanx+tany=tan(x+y)(1-tanxtany)
tan(x-y)=(tanx-tany)/(1+tanxtany),變形：tanx-tany=tan(x-y)(1+tanxtany)
4.萬(wàn)能公式：sin2x=2tanx/(1+(tanx)^2),
cos2x=(1-(tanx)^2)/(1+(tanx)^2)