If one angle of a triangle is greater than the sum of other two so that the triangle is obtuse angle triangle
=> Let ∠A, ∠B and ∠C be the interior angles of ΔABC.
It is given that,
one angle is greater than the sum of the other two angles.
Consider,
∠A > ∠B + ∠C
( ∠A + ∠B + ∠C = 180° )
(∠B + ∠C = 180 - ∠A )
then,
∠A > 180° – ∠A
2∠A > 180°
⇒ ∠A > 90°
Thus, ∠A is an obtuse angle.
Hence, ΔABC is an obtuse angled triangle