**Equation of a Circle**

Starter

Work out how far each of these points is from the origin (0, 0).

(a) (0, 5)

(b) (-5, 0)

(c) (3, 4)

(d) ( 5 , 2 5 )

Examples

Describe the graph with equation

x

+

y

= 7

Find the equation of a circle centred on the origin that passes through the point (2, 6).

The equation of a circle

The equation of a circle centred on the origin is given by

x

+

y

=

r

where

r

is the radius of the circle.

**L.O. - Understand the format for the equation of a circle, and work with circle equations.**

Starter

Work out how far each of these points is from the origin (0, 0).

(a) (0, 5)

(b) (-5, 0)

(c) (3, 4)

(d) ( 5 , 2 5 )

All of them are 5 units away from the origin.

2

2

2

2

2

Examples

Describe the graph with equation

x

+

y

= 7

Circle, centre (0, 0) with radius 7.

Find the equation of a circle centred on the origin that passes through the point (2, 6).

2 + 6 = 40 so equation is

x

+

y

= 40

2

2

2

2

2

2

Activity

Page 373 of Higher tier GCSE book

Plenary

What do you notice?

Does it always happen like this?

Plenary

What do you notice?

It is r

Does it always happen like this?

Yes.

(10, 0)

2

**Activity**

Answers

Answers

**Activities**

**Key Notes**

& Examples

& Examples

**Worked**

Examples

Examples