If A+B+C=180∘A+B+C = 180^\circA+B+C=180∘ for a triangle, which is true?
cos(A+B)=cos(C)\cos(A+B) = \cos(C)cos(A+B)=cos(C)
tan(A+B)=tan(C)\tan(A+B) = \tan(C)tan(A+B)=tan(C)
sin(A+B)=sin(C)\sin(A+B) = \sin(C)sin(A+B)=sin(C)
sin(A+B)=−sin(C)\sin(A+B) = -\sin(C)sin(A+B)=−sin(C)