Definition
Angle addition
Angle addition says adjacent, non-overlapping angle parts add to the whole angle.
What it means
Think of one turn split into pieces. If the pieces sit edge to edge with no gap or overlap, add their degree measures to get the whole turn. You can also subtract a known piece from the whole to find a missing angle.
Remember it
Edge-to-edge angle pieces make one bigger turn, so their measures add.
Example
A 142° angle is split into a 58° part and an unknown part m°. Because 58 + m = 142, m = 84°.
Watch for
The parts must share the same vertex and fill the whole angle without a gap or overlap.
Common mix-up
Angle addition combines angle measures, not the lengths of the rays that draw the angles.
Exact meaning
When adjacent angles share a vertex, do not overlap, and exactly form a larger angle, the measure of the larger angle equals the sum of the measures of its parts.