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# Edexcel C2 Co-ordinate geometry Question Watch

The line PQ is the diameter of the circle, where P and Q are (5, 6) and (-2, 2) respectively. Find the equation of the circle.

Could you show the method where you would find the length of the diameter, then halve it to find the radius, instead of finding the midpoint and the length from the midpoint to one of the points P or Q for the radius.

When i tried it with he first method i got that the lenght of the radius was 5 (finding distance between P and Q and halving)....does anyone know where i went wrong
2. (Original post by THESTRESS)
The line PQ is the diameter of the circle, where P and Q are (5, 6) and (-2, 2) respectively. Find the equation of the circle.

Could you show the method where you would find the length of the diameter, then halve it to find the radius, instead of finding the midpoint and the length from the midpoint to one of the points P or Q for the radius.

When i tried it with he first method i got that the lenght of the radius was 5 (finding distance between P and Q and halving)....does anyone know where i went wrong
First we need to find the midpoint...
For x: (5+-2)/2= 1.5
For y: (6+2)/2= 4
So your midpoint coordinates are 1.5,4

To find r^2: (-2-1.5)^2+(2-4)^2

Then you simply substitute into the circle equation
(x-a)^2+(y-b)^2=r^2
3. (Original post by THESTRESS)

When i tried it with he first method i got that the lenght of the radius was 5 (finding distance between P and Q and halving)....does anyone know where i went wrong
Well, you need to show us your working for us to be able to point out what went wrong.

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