SOLUTION: The greatest angle of a triangle ABC whose sides are a=5, b=5√3 and c=5 ,is ?

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Question 322095: The greatest angle of a triangle ABC whose sides are a=5, b=5√3 and c=5 ,is ?
Answer by Alan3354(69443) About Me  (Show Source):
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The greatest angle of a triangle ABC whose sides are a=5, b=5√3 and c=5 ,is ?
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a = c so it's an isoceles triangle.
b is the longest side, so the angle opposite is the largest.
Use the Cosine Law:
b%5E2+=+a%5E2+%2B+c%5E2+-+2ac%2Acos%28B%29
cos%28B%29+=+%28-b%5E2+%2B+a%5E2+%2B+c%5E2%29%2F%282ac%29
cos(B) = (-75 + 25 + 25)/2*5*5
cos(B) = -25/50 = -0.5
B = 120º