# Circle Equations

## Recognise and use the equation of a circle with centre at the origin and the equation of a tangent to a circle.

##### Level 1Level 2Exam-StyleDescriptionHelpMore Graphs

This is level 1: equations of circles.

 1) Which of the following is the equation of the circle above?a) $$x^2 + y^2 = 16$$b) $$x^2 + y^2 = 4$$c) $$x^2 + y^2 = 8$$ 2) The equation of a circle is $$x^2 + y^2 = 16$$. What is the radius of the circle? 3) The equation of a circle is $$x^2 + y^2 = 30.25$$. What is the radius of the circle? 4) Which of the following is the equation of a circle with centre at the origin and a radius of 14 units?a) $$x^2 + y^2 = 196$$b) $$x^2 + y^2 = 14$$c) $$x^2 + y^2 = 28$$ 5) The equation of a circle is $$5x^2 + 5y^2 = 180$$. What is the radius of the circle? 6) The equation of a circle is $$9x^2 + 9y^2 = 441$$. What is the radius of the circle? 7) Which of the following is the equation of a circle with centre at the origin and a radius of 9 units?a) $$2x^2 + 2y^2 = 81$$b) $$x^2 + y^2 = 9$$c) $$2x^2 + 2y^2 = 162$$ 8) Which of the following is the equation of a circle with centre at the origin which passes through the point (3,4)?a) $$14x^2 + 14y^2 = 25$$b) $$7x^2 + 7y^2 = 175$$c) $$21x^2 + 21y^2 = 25$$ 9) Which of the following is the equation of a circle with centre at the origin and a radius of $$2 \sqrt{2}$$ units?a) $$2x^2 + 2y^2 = 4$$b) $$2x^2 + 2y^2 = 8$$c) $$x^2 + y^2 = 8$$ 10) The equation of a circle is given as $$y^2 = (5+x)(5-x)$$. What is the radius of the circle?
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This is Circle Equations level 1. You can also try:
Level 2

## Instructions

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## Go Maths

Learning and understanding Mathematics, at every level, requires learner engagement. Mathematics is not a spectator sport. Sometimes traditional teaching fails to actively involve students. One way to address the problem is through the use of interactive activities and this web site provides many of those. The Go Maths page is an alphabetical list of free activities designed for students in Secondary/High school.

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## Description of Levels

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Level 1 - Equations of circles

Level 2 - Equations of tangents to circles

Exam Style questions are in the style of GCSE or IB/A-level exam paper questions and worked solutions are available for Transum subscribers.

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## Example

The video above is from the wonderful Corbettmaths.

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