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# Circle Geometry - Can somone help please? watch

1. A circle with centre C, has the equation X^2 + Y^2 -12X +6Y -20=0. Find the centre coordinates and radius. C.T. Square gives (X -6)^2 + (Y+3)^2 = 65.
Now: the origin is the mid point of a chord, show that the gradient of the chord is 2. The grad of 0C is - 1/2 therefore the gradient of the chord using M1xM2 =-1 does equal 2. Now find the distance of o(0,0) to the centre. The distance is 3 root 5 ( 45 ^1/2). Can someone tell me how to find the length of the chord please? Thanks. Dominic
2. Form an equation for the chord using the gradient of the chord and the point you know it passes through. You'll be able to find where it intersects the circle, and using those points you can work out the length of the line.

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