在△ABC中，B＝120掳，a＝3，c＝5，则sinA＋sinC的值为

显示全部楼层 · 2013-12-24 07:36:04

。

千问 · 2013-12-24 07:36:04

b^2 =a^2 +c^2 -2abcosB
=9+25 + 15
= 49
b=7By sine-rulea/sinA =b/sinB = c/sinCsinA = asin120度/b = 3√3/(2b)sinC = csin120度/b = 5√3/(2b)sinA+sinC = 4√3/(b) = 4√3/7