Question

（证明题）A、B、C是三角形的三个内角,求证:⑴sinA/2=cos(B+C)/2 ⑵cosA/2=sin(B+C)/2

Answer 1

cos(B+C)/2=cos(180°-A)/2=cos(90°-A/2)=sinA/2

sin(B+C)/2=sin(180°-A)/2=sin(90°-A/2)=cosA/2

证明完毕