<Dd> h = 1 2 4 a 2 − b 2 . (\ displaystyle h = (\ frac (1) (2)) (\ sqrt (4a ^ (2) - b ^ (2))).) </Dd> <P> This formula can also be derived from the Pythagorean theorem using the fact that the altitude bisects the base and partitions the isosceles triangle into two congruent right triangles . </P> <P> The Euler line of any triangle goes through the triangle's orthocenter (the intersection of its three altitudes), its centroid (the intersection of its three medians), and its circumcenter (the intersection of the perpendicular bisectors of its three sides, which is also the center of the circumcircle that passes through the three vertices). In an isosceles triangle with exactly two equal sides, these three points are distinct, and (by symmetry) all lie on the symmetry axis of the triangle, from which it follows that the Euler line coincides with the axis of symmetry . The incenter of the triangle also lies on the Euler line, something that is not true for other triangles . If any two of an angle bisector, median, or altitude coincide in a given triangle, that triangle must be isosceles . </P> <P> The area T (\ displaystyle T) of an isosceles triangle can be derived from the formula for its height, and from the general formula for the area of a triangle as half the product of base and height: </P>

An isosceles triangle has two sides of equal length