As an 8th Grader in Algebra One, A 180* Angle is a straight line!! How to Prove this: Draw a circle. Divide it into equal fourths. Write (Top,Right, Bottom, left) 0 AND 360, 90, 180, 270. These, as a aviation expert, are called "degrees". They show you what direction your facing, also used as a protractor. For instance, 0 is North, 90 is East, 180 is south, 270 is west, and 360 is North. Now, take a random number from this chart. (90,180,0,360,270)Subtract another number, and take that numbers absolute value (The distance between that number and 0) and remember that number. What can be proven? Numbers adjacent to each other are ALWAYS equal to 90, (unless its 360-90 or 0-270, but 0 and 360 are the same cardinal degree, so thats why the numbers are confusing here.) and numbers opposite another are ALWAYS equal to 180. (These numbers are the angle. I.e, 180 is a 180degree angle)Now, connect those two numbers using a line. The angle is 180, and the line you draw is straight!! This can only be explained by ONE reason!! A 180 Degree angle IS A STRAIGHT LINE!! *Gasp!