Circle · Second Year
Circle
Second Year · Circumference & area · Tap NEXT to begin
Section 1 of 2
The Parts of a Circle
The radius runs from the centre to the edge and never changes; the diameter is twice the radius.
Words to know
Centre · radius $r$ · diameter $= 2r$ · circumference (the length round) · chord · arc · sector · segment.
Section 2 of 2
Circumference & Area
The two formulas (in your tables)
Circumference $\ell = 2\pi r$. Area $A = \pi r^2$. Use $\pi = \tfrac{22}{7}$, $3.14$, or the calculator button.
Now you try
You try
Find the circumference of a circle of radius $7$ cm, using $\pi = \tfrac{22}{7}$.
Pen and paper out — try it before you reveal.
$\ell = 2\pi r = 2\times\tfrac{22}{7}\times 7$
$\ell = 44$ cm
$\ell = 44$ cm
You try
Find the area of a circle of radius $7$ cm, using $\pi = \tfrac{22}{7}$.
Pen and paper out — try it before you reveal.
$A = \pi r^2 = \tfrac{22}{7}\times 7^2 = \tfrac{22}{7}\times 49$
$A = 154\ \text{cm}^2$
$A = 154\ \text{cm}^2$
That’s the Circle.
The parts, plus $\ell = 2\pi r$ and $A = \pi r^2$ — both in your tables.