Let's consider the triangle whose interior angles are ∠2, ∠3, and ∠4.
On the figure, the red marker indicates that the two lines are perpendicular. This means that ∠4 is a right angle.
m∠4=90
According to Corollary 4.2 to the Triangle Angle-Sum Theorem, the other two angles, ∠2 and ∠3, must be acute. Therefore, out of these three angles, ∠4 has the greatest measure.
