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# Core 1 help watch

1. Find the equation of the circle with centre(4,0) and radius 3,giving your answer in multiplied out term.
The straight line y= kx, where k is a constant,meets the circle in part(i).
(ii) Show that the x-co-ordinates of the points of intersection are given by the equation: (k^2+1)x^2 - 8x + 7 = 0.
2. (X-*)^2 + (y+*)^2 = r^2
Substitute the values, then expand it and substitute y for kx and expand again if necessary
3. (Original post by zayn008)
(X-*)^2 + (y+*)^2 = r^2
Substitute the values, then expand it and substitute y for kx and expand again if necessary
If i substitute y for kx i get (x-4)^2 + (kx)^2 = 9
If i expand this and put everything to one side, i get x^2 + y^2 - 8y + 7 + k^2x^2 = 0.
Do i put this into the brackets again to get the answer they want??
4. (Original post by Chelsea12345)
If i substitute y for kx i get (x-4)^2 + (kx)^2 = 9
If i expand this and put everything to one side, i get x^2 + y^2 - 8y + 7 + k^2x^2 = 0.
Do i put this into the brackets again to get the answer they want??
yep! It should be -8x not -8y, simply factor out x^2 and you've got the answer they're looking for

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