Sum of all angles is  180°. The area of a triangle can be solved with the formula[br][br]  [math]\LARGE A=\frac{1}{2}ah,[/math][br][br]where [i]a[/i] is the base of the triangle and [i]h[/i] is the perpendicular height of the triangle.[br][br]There are three special cases of triangles and all of them have features simplifying solving:[br][list][*][color=#0000ff]equilateral triangle[/color]: all sides are equal and all angles are 60°. [br] [/*][*][color=#0000ff]isosceles triangle[/color]: two sides of a triangle equal. Thus, base angles are also equal. [br] [/*][*][color=#0000ff]right-angled triangle[/color]: one angle is 90°.[br] [/*][/list]The height of an isosceles or an equilateral triangle bisects the base into two equal parts. [br][br]Identifying the parts of a triangle must be done in a systematic way: a vertex is marked with uppercase letters (e.g. A), the corresponding lowercase letter for the side opposite the vertex (a), and the angle at the vertex is marked with a corresponding greek letter ([math]\Large\alpha[/math] ). Identifying is done anticlockwise.[br][br]