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# Test yourself now

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## 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 $$= \pi r^2$$.