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[[Image:Rtriangle.svg|thumb|A typical right triangle]]

[[Image:Rtriangle.svg|thumb|A typical right triangle]]

A '''right triangle''' has three sides and an angle that equals 90º.

A '''right triangle''' (or '''right-angled triangle''', more commonly in [[British English]]) has three sides, with an angle that equals 90º - that is, a [[right angle]].

The general right triangle is the subject of one of the more famous mathematical ideas, the [[Pythagorean Theorem]].  It states that the sum of the squares on the legs (short sides) of a right triangle is equal to the square on the hypotenuse (the long side, opposite the right angle).  Using the figure to the right, this means:

The general right triangle is the subject of one of the more famous mathematical ideas, the [[Pythagorean Theorem]].  It states that the sum of the squares of the legs (short sides) of a right triangle is equal to the square on the [[hypotenuse]] (the long side, opposite the [[right angle]]).  Using the figure to the right, this means:

:<math>a^2 + b^2 = c^2</math>

:<math>a^2 + b^2 = c^2</math>

The analysis of ratios between sides of right triangles with hypotenuse = 1 is at the heart of [[trignometry]].

The analysis of ratios between sides of right triangles with hypotenuse = 1 is at the heart of [[trigonometry]]. The [[sine]] of the angle at A is determined as the ratio of a/c, the [[cosine]] as b/c and the [[tangent]] as a/b. Relative to the angle A, the side ''b'' is described as the adjacent side and ''a'' as the opposite side.

[[category:geometry]]

[[Category:Plane Geometry]]