## 16.9 Chapter summary

- Perimeter is the total distance around the outside of a shape.
- Area is the total space or surface of a flat shape.
- Perimeter of a square \(= 4s\).
- Area of a square \(= s^2\).
- Perimeter of a rectangle \(= 2l + 2b\).
- Area of a rectangle \(= l \times b\).
- Perimeter of a scalene triangle \(= a + b + c\).
- Perimeter of an isosceles triangle \(= 2a + b\).
- Perimeter of an equilateral triangle \(= 3a\).
- The perpendicular height of a triangle is the perpendicular line drawn from the opposite vertex to the base of the triangle.
- Area of a triangle \(= \frac{1}{2} (b \times h)\).
- The perimeter of a circle is called its circumference.
- The centre of a circle is the point inside the circle that is equidistant from all points on the circumference of the circle.
- A line segment drawn from one point on the circumference to another point on the circumference that passes through the centre is called a diameter.
- A line segment from the centre of the circle to a point on the circumference is called a radius.
- The diameter of a circle is equal to twice its radius (\(d = 2r\)).
- The ratio of the circumference of a circle to its diameter is the mathematical constant, pi (\(\pi\)).
- For everyday use in calculations we use the approximate rational value \(\pi = \frac{22}{7}\) or \(\pi = \text{3,14}\).
- Circumference of a circle \(C = \pi d = 2 \pi r\).
- Area of a circle \(= \pi r^2\).