## triangleacute, obtuse, or right;
or by their sides, as scalene (all different), isosceles (two the same), or equilateral (all equal). A right (or
right-angled) triangle has one interior angle equal to 90°, and may
be either scalene or isosceles (see Pythagoras'
theorem). Various formulae link the dimensions of a triangle (see diagram). The cosine formula states that a^{ 2} = b^{ 2} + c ^{2} - 2bc cos A, and the sine formula that a / sin A = b / sin B = c / sin C. If s = 1/2 (a + b + c), the area of the triangle is √[s(s - a)(s - b)(s - c)]. ## Other types of triangleAPythagorean triangle is a right triangle whose sides are integers. A primitive Pythagorean
triangle is one whose sides are relatively
prime. A medial triangle is a triangle whose vertices are the midpoints of the sides of a given triangle. An orthic triangle is a triangle whose vertices are the feet
of the altitudes of a given triangle. A limping triangle is right triangle whose two shorter sides
(i.e., those other than the hypotenuse) differ in length by one unit. An
example is the 20-21-29 triangle (20^{2} + 21^{2} = 29^{2}). The pedal triangle of a point P with respect to a triangle ABC is the triangle whose vertices are the feet
of the perpendiculars dropped from P to the sides of triangle ABC. ## Related category• POLYGONS | ||||||

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