The horizontal value in a pair of coordinates: how far along the point is. The X Coordinate is always written first in an ordered pair of coordinates (x,y), such as (12,5). In this example, the value "12" is the X Coordinate.
Angel b=angle a+angle c-180
We have now proven that all three angles of ΔABC have a measure of 60 degrees. Therfore, ∠C must have a measure of 60 degrees