4.2

According to Theorem 4.1 (Angle Sum)
The measures of the angles in a triangle are always equal to 180
m

If we know the measures of two angles, we can find the third measure.

if two angles of one triangle are congruent to two angles of another triangle, then the third angles of the triangles are not congruent.

Exterior Angle Theorem
The measure of one exterior is equal to the two interior angle measures added together.

A corollary is a statement that is easily proven with a theorem.
Corollary 4.1: acute angles of right triangles are always complimentary.
Corollary 4.2: there can only be one right angle or one obtuse angle in a triangle.