Give the center & radius of circle: (x+3)^2 + (y-1)^2=16       

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aliddi's profile pic

aliddi | High School Teacher | (Level 1) Adjunct Educator

Posted on

An easy way to remember is to change the sign of the numbers h and k as described in the previous response.  If they are negative, make them positive, if they are positive, make them negative. Remember to write this as a coordinate.

So, the center would be (-3, 1)

Also, to find the radius find the square root of the number the equation is set equal to.

So, the radius would be 4.

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted on

A circle with center (h, k) and radius has an equation (x - h)^2 + (y - k)^2 = r^2.

The circle we are given here is (x+3)^2 + (y-1)^2=16

=> (x - (-3))^2 + (y - 1)^2 = 16

=> (x - (-3))^2 + (y - 1)^2 = 4^2

This gives h = -3, k = 1 and r = 4

The center of the given circle is (-3 , 1) and the radius is 4.

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