Right angles

In geometry and trigonometry, a right angle is an angle of exactly 90° (degrees), corresponding to a quarter turn. If a ray is placed so that its endpoint is on a line and the adjacent angles are equal, then they are right angles. The term is a calque of Latin angulus rectus; here rectus means "upright", referring to the vertical perpendicular to a horizontal base line.

Closely related and important geometrical concepts are perpendicular lines, meaning lines that form right angles at their point of intersection, and orthogonality, which is the property of forming right angles, usually applied to vectors. The presence of a right angle in a triangle is the defining factor for right triangles, making the right angle basic to trigonometry.

A rectangle is a quadrilateral with four right angles. A square has four right angles, in addition to equal-length sides.

The Pythagorean theorem states how to determine when a triangle is a right triangle.

In Unicode, the symbol for a right angle is U+221F ∟ Right angle (HTML ∟). It should not be confused with the similarly shaped symbol U+231E ⌞ Bottom left corner (HTML ⌞). Related symbols are U+22BE ⊾ Right angle with arc (HTML ⊾), U+299C ⦜ Right angle variant with square (HTML ⦜), and U+299D ⦝ Measured right angle with dot (HTML ⦝).

...
Wikipedia