(1)
ABC成等差数列, A+B+C =3B =180度
B=60度 , A+C =120度
(1/2)a,b,3c成等比数列
b^2= 3ac/2
ac=(2/3) b^2
正弦定理 SinA/a =SinB/b =SinC /c
SinA SinC = (2/3) (SinB)^2 = 1/2
2SinA Sin(120-A) =1
积化和差:
Cos(2A-120) - Cos(120) =1
Cos(2A-120) =1 + (-1/2) =1/2
2A-120 = ±60
A=60±30
A=30 或 90 度
(2)
A =30度, a=1
B=60, C=90
三角形完全确定,何来最大值?
追问啊大神啊还有两题求助!
![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/5d6034a85edf8db17b8ba5430b23dd54564e7474?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
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追答晕,你照相手发抖吗?好难看清楚呀:)
sinA +sinC = (3+ √7)sinB ,
sinA =3sinB
求 C
不知道是不是这样?
追问![](https://video.ask-data.xyz/img.php?b=https://iknow-pic.cdn.bcebos.com/d0c8a786c9177f3e5834b22172cf3bc79f3d569d?x-bce-process=image%2Fresize%2Cm_lfit%2Cw_600%2Ch_800%2Climit_1%2Fquality%2Cq_85%2Fformat%2Cf_auto)
求答案啦