Question

在△ABC中,下列等式成立的是A.sin(A+B)=sinCB.cos(b+c)=cosAC.tan(A+B)/2=ta

Answer 1

cos(B+C)=cos(180-A)=-cosA

tan(A+B)/2=tan(90-C/2)=cotC/2

sin(B+C)/2=sin(90-C/2)=cosC/2

所以BCD都错

sin(A+B)=sin(180-C)=sinC

选A