SOLUTION: if one angle of a triangle is greater than the sum of the other two, show that the triangle is obtuse angle

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Question 639895: if one angle of a triangle is greater than the sum of the other two, show that the triangle is obtuse angle
Answer by Edwin McCravy(20054)   (Show Source): You can put this solution on YOUR website!

Given:  ᐃABC 
       ∠A > ∠B + ∠C

∠A + ∠B + ∠C = 180°           Sum of the angles of a triangle.
     ∠B + ∠C < ∠A             Reversal property of the given inequality
∠A           > 180° - ∠A      differences of unequals subtracted from equals
                               are unequal in the reverse order.
    ∠A + ∠A > 180°             Adding ∠A to both sides (adding =s to =s)
        2∠A > 180²             1+1=2
         ∠A > 90°              Equals divided by equals

ᐃABC is an obtuse triangle    It has an angle > 90°  

Edwin
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