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 $= \pi r^2$.