A triangle is any shape that has exactly three straight sides and three angles. A feature of all triangles is that the angles within the triangle always add up to 180ᵒ.
There are special triangles that have additional features that you will be expected to know if they are mentioned.
First, we have an Isosceles triangle that will have two sides that are the same length and therefore two angles that are equal.
Second, we have an Equilateral triangle that has dashes on all the sides, meaning all the sides are the same length, and therefore all the angles are equal to each other. In this particular triangle all the angles are 60ᵒ.
Our third triangle is one that you will encounter on a regular basis, a right-angled triangle (the little square denotes which of the angles is 90ᵒ).
A quadrilateral is any shape with four straight sides and four angles. There are many special types of quadrilateral and they are dealt with in more detail in our lessons on shapes.