m∠1 + m∠2 = m ∠4 , under the exterior angle property of a triangle which says that sum of the interior opposite angles of an exterior angle will be equal to the measure of the exterior angle .
To prove that m∠3 + m ∠1 + m∠2 = 180° , let us use the angle sum property .
= Angle sum property = Sum of the three interior angles in a triangle will be equal to 180° .
= Since ∠1 , ∠2 and ∠3 are the interior angles of this triangle , their sum will be equal to 180° .
Hence proved that m∠1 + m∠2 + m∠3 = 180°
∴ m∠1 + m∠2 + m∠3 = 180° under the angle sum property of a triangle .
