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两角和公式
sin(A B)=sinAcosB cosAsinB sin(A-B)=sinAcosB-sinBcosA
cos(A B)=cosAcosB-sinAsinB cos(A-B)=cosAcosB sinAsinB
tan(A B)=(tanA tanB)/(1-tanAtanB) tan(A-B)=(tanA-tanB)/(1 tanAtanB)
ctg(A B)=(ctgActgB-1)/(ctgB ctgA) ctg(A-B)=(ctgActgB 1)/(ctgB-ctgA)