已知角ABC的三个内角A,B,C满足2B=A+C,三边a,b,c的倒数满足2/b=1/a+1/c,求角A,B,C的大小
问题描述:
已知角ABC的三个内角A,B,C满足2B=A+C,三边a,b,c的倒数满足2/b=1/a+1/c,求角A,B,C的大小
答
2B=A+C 且A+B+C=180 得B=60,A+C=120…………(1)
sinA/a=sinB/b=sinC/c
设sinA/a=sinB/b=sinC/c=t =〉1/a=t/sinA,1/b=t/sinB,1/c=t/sinC
代入可得2/sinB=1/sinA+1/sinC…………(2)
联立(1)(2)得
A=B=C=60