Question

数学三角函数已知A,B,C是三角形ABC的内角,下列不等式正确的是:1.sin(A+B)=sinC 2.cos(A+B)

Answer 1

sinC=sin[兀-(A+B)]=sin(A+B)

cosC=cos[兀-(A+B)]=-cos(A+B)

tanC=tan[兀-(A+B)]=-tan(A+B)

cosA/2=cos{[兀-(B+C)]/2}=cos[兀/2-(B+C)/2]=sin[(B+C)/2]

所以1正确