What are supplementary estimates?

Supplementary angles - two angles that add up to 180 degrees.

No matter how large or small angles 1 and 2 on the left become, the two angles remain supplementary which means that they add up to 180°.

By the way, supplementary angles do not need to be adjacent angles(angles next to one another) if it doesnt add up to 180 then they are not supplementary angles, but if they do then they are supplementary angles.