How many undeveloped corners are formed when two straight lines intersect?

Flattened angle – an angle whose sides form a straight line. An unfolded angle is 180 °, therefore, an unfolded angle is an angle whose degree measure is not 180 ° (more or less).
When two straight lines intersect, four angles are formed, the degree measure of which is different from 180 °, the sum of these angles is 360 °. Let us denote all these angles as ∠1, ∠2, ∠3 and ∠4. Pairs of angles ∠1 and ∠3, ∠2 and ∠4 are vertical angles, their degree measure is equal to. Pairs of angles ∠1 and ∠2, ∠2 and ∠3, ∠3 and ∠4, ∠1 and ∠4 are adjacent, their sum is 180 °.