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kumar69

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

  • 11 months ago
  • 11 months ago

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  1. RolyPoly
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    Can you please double check the question? Is it "-AB.AC" instead of "+AB.AC" ?

    • 11 months ago
  2. RadEn
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    use the cosine rule : |dw:1368950431568:dw| cos60 = (AB^2 + AC^2 - BC^2)/2ABAC

    • 11 months ago
  3. RadEn
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    1/2 = (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

    • 11 months ago
  4. RadEn
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    cross product out! AB * AC = AB^2 + AC^2 - BC^2

    • 11 months ago
  5. RadEn
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    and actually, Rolypoly is right, that should "-AB.AC" not +AB AC i think there is a bit typo from u, @kumar69

    • 11 months ago
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