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# Equations of circles & intersects Watch

1. Hi I have the following questions;

the circle C has center (-1,6) and a radius 2root5 form equations c:

so (x+1)^2+(y-6)^2=20

The line y=3x-1 intersects C at the points A and B

find the coordinates of A and B

so I substituted y=3x-1 into the circle formula and got 10x^2-30x+30=0 then I factorised to get (x-3)(x-1). I'm unsure of what to Do next
2. (Original post by berwick53)
Hi I have the following questions;

the circle C has center (-1,6) and a radius 2root5 form equations c:

so (x+1)^2+(y-6)^2=20

The line y=3x-1 intersects C at the points A and B

find the coordinates of A and B

so I substituted y=3x-1 into the circle formula and got 10x^2-30x+30=0 then I factorised to get (x-3)(x-1). I'm unsure of what to Do next
You have the x-coordinates of the points of intersection (the solutions of ), so now just find the corresponding y-coordinates.

Note that it'll be a lot easier to find the y values by substituting into the equation of the line rather than from the more complicated equation that the circle has.

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Updated: December 6, 2010
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