A right angle is an angle that measures exactly 90 degrees.

A right angle is an angle equal to half the angle from one end of a line segment to the other. A right angle is π/2 radians or 90°. A triangle containing a right angle is called a right triangle. However, a triangle cannot contain more than one right angle, since the sum of the two right angles plus the third angle would exceed the 180° total possessed by a triangle. The patterns of cracks observed in mud that has been dried by the sun form curves that often intersect in right angles.

acute angle | full angle | gnomon | oblique angle | obtuse angle | orthogonal lines | perpendicular | right triangle | semicircle | straight angle | Thales' theorem

elementary school level (California grade 3 standard)