Question

三角形ABC中，a,b,c是A,B,C所对的边，S是该三角形的面积，且cosB/cosC=—（b/（2a+c）。(1)求角B

在三角形ABC中角A,B,C所对的边分别为a,b,c，S，为该三角形的面积，且cosB/cosC=—（b/（2a+c）。(1)求角B.。（2）若a=4,S=3√5，求b

Answer 1

Riley went to the Miami Heat training camp guide

Riley

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"I asked them, 'Why are you currently not within the initial round or second round choose?'" Riley said, "if in the chance, I'm prepared to use front of every of them, tell them, 'only one reason, and that is where you'll need to improve 'I think we will try to help them to find flaws, to find out to fix this problem, their lives will turn for that better. "Riley believes that next season the Heat have still speed, he chose rookie point guard Norris - Kaul is perfect for this consideration. Riley and also the Heat coach Erik - Spoelstra to satisfy and talk about the Miami Heat next season, the Department can be improved,authenic nike air max, "Eric and i also sat down and chatted, we talked about all of the things this year,Nike Air Max 95, but additionally about to areas in which we can become much better. he and I agree is that the Heat need to improve speed, reaction, athleticism, and so on. "

Heat next season's team are those people? Riley mentioned by name six will be, "We continues to LeBron - Lebron, Dwyane - Wade, Chris Bosh -, - Mario Chalmers - Joel Anthony and Norris (Kaul) is team,Nike Air Max 2010, they are our veins like blood. As for the rest of the lineup,Nike Air Max 87, it's feasible we are going to make adjustments. "As the Miami Heat last season, just a thin two wins from winning it, so Riley the team don't do an excessive amount of alter, Riley analysis, "At this moment, we pointed out that we get from your championship just two wins merely a thin, we require to accomplish the beating of the alter,TN Shoes at wholesale price, we just need to know the opportunities it may."

追问

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Answer 2

边化角或者角化边，再用正余弦定理，还有S=0。5*ab*sinC面积公式

Answer 3

1
a/sinA=b/sinB=c/sinC=k
cosB/cosC=-b/(2a+c)
cosB/cosC=-sinB/(2sinA+sinC)
cosBsinC+2sinAcosB=-sinBcosC
sinA=-2sinAcosB
cosB=-1/2
b=120

2
c=2S/asinB=6√5/(2√3)=√15
b^2=a^2+c^2-2accosB
=16+15+4√15
=31+4√15
b=√(31+4√15)