As we know that the standard equation of circle is 
, where <em>r</em> is the radius of circle and centre at <em>(h,k) </em>
Now , as the circle passes through <em>(2,9)</em> so it must satisfy the above equation after putting the values of <em>h</em> and <em>k</em> respectively
After raising ½ power to both sides , we will get <em>r = +5 , -5</em> , but as radius can never be -<em>ve</em> . So <em>r = +</em><em>5</em><em> </em>
Now , putting values in our standard equation ;
<em>This is the required equation of </em><em>Circle</em>
Refer to the attachment as well !
I'm thinking maybe x is supposed to represent the number of tasks completed because it states Shelly earned 90 points on each task. Then when put together it may look like this, let's say there are 4 tasks= Ex.90 times the 4 tasks minus 20 points which would total the points Terrence's has earned. So i believe x is the total tasks. Hope I didn't make it confusing...
Her position is at (6,9/2)
Center will be (6,-4) and the radius will be square root of 7
