# Homework Help: Finding co-ordinates in squares

1. Oct 4, 2004

### bob4000

urgent!!!!! finding co-ordinates in squares

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

equation BD is y=3x-9

midpoints AC: (4,3)

find the co-ordinates of B and D

i just dont understan how to get the co-ordinates, ive tried plotting a graph but to no avail. i found the midpoints and the equation listed above with relative ease but this part of the question just baffles me. if anyone could just explain the method of this kind of task, i will be able to answer the question. thank you.

2. Oct 4, 2004

### Tide

It might help to use the fact that the product of the slopes of the diagonals is -1.

3. Oct 4, 2004

### bob4000

i used tht to find the equation, but i dont see how that can help me with the co-ordinates?

4. Oct 4, 2004

### Tide

It's even easier than I thought. The diagonals have the same midpoint and the distances from the midpoint to each corner are all the same.

5. Oct 4, 2004

### bob4000

i think i get it now. thanks alot