IXL - Find the radius or diameter of a circle (Geometry practice)

What is the radius of this circle?

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Learn with an example

question

What is the radius of this circle?

key idea

A circle is the set of points in a plane that are the same distance from a fixed point. The distance is the

radius.

The point is the

center.

solution

To find the radius, locate the center and a point on the circle. Calculate the distance between the center and that point.

Locate the center and a point on the circle.

Look at the graph:

(

)

is the center and

(

)

is a point on the circle.

Calculate the distance.

Since

(

)

and

(

)

have the same

-coordinate,

0, the distance between them is the absolute value of the difference in their

-coordinates:

–

The radius is 4.

Looking for more? Try these:

Lesson: Equations of circles

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Teacher tools

Work it out

Not feeling ready yet? These can help:

Y.1Find the center of a circle

M.4Distance between two points

E.1Square roots of perfect squares

Lesson: Equations of circles

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