sin(A+B)=sinAcosB+cosAsinBZmD
sin(A-B)=sinAcosB-sinBcosA
cos(A+B)=cosAcosB-sinAsinB9 9 x i n x i n e t
cos(A-B)=cosAcosB+sinAsinB
tan(A+B)=(tanA+tanB)/(1-tanAtanB)9+9+信+息+网
tan(A-B)=(tanA-tanB)/(1+tanAtanB)
cot(A+B)=(cotAcotB-1)/(cotB+cotA) 9+9+信+息+网
cot(A-B)=(cotAcotB+1)/(cotB-cotA)
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