Explanation:
A pair of Supplementary angles
Supplementary
angles are pairs of angles that add up to 180 degrees. (Our solved example in mathguru.com uses this concept)
If the two
supplementary angles are adjacent (i.e. have a common vertex and share just one side), their
non-shared sides form a line. The supplement of an angle of 135 degrees is an angle of 45
degrees. The supplement of an angle of x degrees is an angle of
(180 − x) degrees. Supplementary angles do not have to
be on the same line, and can be separated in space. For example, adjacent
angles of a parallelogram are supplementary.
http://en.wikipedia.org/wiki/Supplementary_angles
Vertical angles
Two
lines intersect to create two pairs of vertical angles. One pair consists of
angles A and B; the second pair consists of angles C and D.
In geometry, a pair of angles is said to be vertical (also opposite and vertically opposite, which is abbreviated as vert. opp. ∠s) if the angles are formed
from two intersecting lines and the angles are not adjacent. They all share a vertex. Such
angles are equal in measure and can be described as congruent. (Our solved example in mathguru.com uses this concept)
http://en.wikipedia.org/wiki/Vertical_angles
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