Circle Equations

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

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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 12 units?a) $$x^2 + y^2 = 144$$b) $$x^2 + y^2 = 12$$c) $$x^2 + y^2 = 24$$ 5) The equation of a circle is $$3x^2 + 3y^2 = 75$$. What is the radius of the circle? 6) The equation of a circle is $$8x^2 + 8y^2 = 128$$. 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 6 units?a) $$2x^2 + 2y^2 = 36$$b) $$x^2 + y^2 = 6$$c) $$2x^2 + 2y^2 = 72$$ 8) Which of the following is the equation of a circle with centre at the origin which passes through the point (3,4)?a) $$6x^2 + 6y^2 = 25$$b) $$3x^2 + 3y^2 = 75$$c) $$9x^2 + 9y^2 = 25$$ 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 $$y^2 = (4+x)(4-x)$$. What is the radius of the circle?
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This is Circle Equations level 1. You can also try:
Level 2

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Level 1 - Equations of circles

Level 2 - Equations of tangents to circles

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