Based on the Exterior Angle Property of Triangles, we have been able to prove that m∠1 = m∠3 + m∠4. Thus, option B is the answer.
What is the Exterior Angle Property of Triangles?
The Exterior Angle Property of Triangles states that in a triangle, the measure of an exterior angle is congruent to the sum of the measures of its two remote interior angles.
Thus, we can state the following:
The sum of the interior angle measures of a triangle must be equal to 180 degrees.
So, we would have, m∠2 + m∠3 + m∠4 = 180 degrees.
Given that m∠2 = 30°, so:
m∠3 + m∠4 = 150°
Looking at the figure, m∠1 + m∠2 = 180°.
Since m∠2 = 30°, it must be that m∠1 = 180 - 30 = 150°
Therefore, m∠1 = m∠3 + m∠4 (since m∠3 + m∠4 = 150° and m∠1 = 150°).
This can be said to be as a an example of the Exterior Angle Property of Triangles which states that: the measure of an exterior angle of any triangle option B.