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# Find the coordinates of B & D. watch

1. OCR C1, Misc Ex 1, p23.

4. A(7, 2) and C(1, 4) are to vertices of a square ABCD.

(a) Find in the form of ax + by = c the equation of the diagonal BD

Calculated equation for line AC, used perpendicular gradient and added the midpoint of AC as x & y to get c.. so 3x - y = 9 (thrown my workings in the bin o.O sorry!)

(b) Find the coordinates for B and D..

I can't for the life of me get my head around this one.. I think I'm just having a mental blank.. can somebody help me out?

Thx..
2. Since it's a square, B is equidistant to A and C. B is also on the same horizontal line as A, and the same vertical line as C. You can use this information and the equation for AC to work out the coordinates of B. Do a similar thing for D.

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Updated: March 29, 2011
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