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kumar69
 2 years ago
In triangle ABC, angleA=60 degree, prove that BC2=AB2+AC2+AB.AC
kumar69
 2 years ago
In triangle ABC, angleA=60 degree, prove that BC2=AB2+AC2+AB.AC

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RolyPoly
 2 years ago
Best ResponseYou've already chosen the best response.1Can you please double check the question? Is it "AB.AC" instead of "+AB.AC" ?

RadEn
 2 years ago
Best ResponseYou've already chosen the best response.0use the cosine rule : dw:1368950431568:dw cos60 = (AB^2 + AC^2  BC^2)/2ABAC

RadEn
 2 years ago
Best ResponseYou've already chosen the best response.01/2 = (AB^2 + AC^2  BC^2)/2*AB*AC multiplify by 2 to both side, giving us 1 = (AB^2 + AC^2  BC^2)/AB*AC

RadEn
 2 years ago
Best ResponseYou've already chosen the best response.0cross product out! AB * AC = AB^2 + AC^2  BC^2

RadEn
 2 years ago
Best ResponseYou've already chosen the best response.0and actually, Rolypoly is right, that should "AB.AC" not +AB AC i think there is a bit typo from u, @kumar69
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