Using the formula for the area of a circle | Maths | Quizalize & Oak National Academy

Starter quiz

Match the parts of a circle with their descriptions.

circumference

⇔

the distance around the edge of a circle ✓

diameter

⇔

furthest distance from one side of a circle to the other ✓

radius

⇔

any line segment from centre to circumference of circle ✓
What is 10 $\pi$ as a decimal rounded to 3 significant figures?

'31.4' ✓
Evaluate the expression $5x^2$ when $x=2$ .

'20' ✓
Solve the equation: $4x^2 = 36$

'3' ✓
Which is the formula for the area of a circle?

$A = \pi r$

$A = 2\pi r$

$A = \pi r2$

$A = \pi r^2$ ✓

$A = \pi^2 r$
What is the area of the circle?

$9 \pi$ cm $^2$

$18 \pi$ cm $^2$

$81 \pi$ cm $^2$ ✓

$324 \pi$ cm $^2$

The area of a circle can be calculated by multiplying $\pi$ by the square of the ______.

'radius' ✓
A circle has radius 10 cm. Its area is ______ cm $^2$ , when rounded to 3 significant figures.

'314' ✓
The area of the circle is ______ cm $^2$ .

6 $\pi$

9 $\pi$ ✓

12 $\pi$

36 $\pi$
The distance from the centre of a circle to its edge is 12 cm. The area of the circle is ______ $\pi$ cm $^2$ .

'144' ✓
The area of a circle is 80 cm $^2$ . The radius is ______ cm, when rounded to 3 significant figures.

2.85

5.05 ✓

10.1

25.5
The area of a circle is 150 cm $^2$ . The diameter is ______ cm, when rounded to 3 significant figures.

3.45

6.91

13.8 ✓

47.7

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When calculating the diameter, pupils may use rounded numbers to perform subsequent calculations.

Repeat one of the demonstrations of finding the diameter but round each decimal as they appear and compare the accuracy of the final answer.

Area - Area is the size of the surface and states the number of unit squares needed to completely cover that surface.
Radius - The radius of a circle is any line segment that joins the centre of a circle to its edge.
Diameter - The diameter of a circle is any line segment that starts and ends on the edge of the circle and passes through the centre.