Right angle
A right angle is the angle formed by two perpendicular lines. The measure of every right angle is 90 degrees or 
radians. When drawing diagrams, we denote right angles with a little square:
![[asy] unitsize(2cm); pair A, B, C, D, I; A = (1, 0); B = (-1, 0); C = (0, 1); D = (0, -1); I = (0, 0); draw(A--B, Arrows); draw(C--D, Arrows); draw(rightanglemark(C, I, A, 5)); [/asy]](http://latex.artofproblemsolving.com/9/9/1/991a66b234c3f63b1f9af7a3a50587d604540e7f.png)
See Also
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