An isosceles triangle is a triangle with (at least) two equal sides. In the figure above, the two equal sides have length and the remaining side has length . This property is equivalent to two angles of the triangle being equal. An isosceles triangle therefore has both two equal sides and two equal angles. The name derives from the Greek iso (same) and skelos (leg). The height of the isosceles triangle illustrated above can be found from the Pythagorean theorem as The area is: The perimeter is: Trigonometric functions of half angles in a triangle