Straight angle
A straight angle is an angle in which the two sides of the angle lie along a single line, pointing in opposite directions. The measure of every straight angle is 180 degrees or 
radians.
![[asy] pair A, B, I; A = (-1, 0); B = (1, 0); I = (0, 0); draw(A--B, Arrows); draw(anglemark(B, I, A, 4)); label("$180^\circ$", I, 4N); [/asy]](http://latex.artofproblemsolving.com/7/8/d/78d8f2250fed7b456c1e695a93d86d533b480f93.png)
See Also
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