Isosceles triangle

{{Infobox polytope The isosceles triangle, or isot, is a type of triangle with two of the three side lengths equal, as are two of the three angles. It can be considered as a pyramid where the base is a dyad.
 * dim = 2
 * obsa = Isot
 * edges = 1+2
 * img=Isosceles triangle.svg
 * vertices = 1+2
 * verf = Dyad
 * coxeter = ox&#y
 * symmetry = A1×I, order 2
 * army=Isot
 * reg=Isot
 * els=b [base], ℓ [legs]
 * circum=$$\frac{l^2}{2\sqrt{l^2-\frac{b^2}{4}}$$
 * area=\frac{b}{2}\sqrt{l^2-b^2/4}
 * angle=base–leg: $$\arccos\left(\frac{b}{2l}\right)$$
 * angle2=leg–leg: $$2asin(\frac{b}{2l}\right)$$
 * dual=Isosceles triangle
 * conjugate=Isosceles triangle
 * conv = Yes
 * off = isot.off
 * orientable = Yes
 * nature = Tame}}

Its unequal side is often called its base, in analogy to the pyramid construction. Its equal sides are called its legs.

Vertex coordinates
Coordinates for an isosceles triangle with base length b and leg length ℓ are given by:
 * (±b/2, 0),
 * (0, $\sqrt{ℓ^{2}–b^{2}/4}$).

In vertex figures
All regular polygonal prisms have an isosceles triangle for a vertex figure. Polyhedra with isosceles vertex figures are sometimes known as truncated regular polyhedra, as they all derive from truncations of other polyhedra.