Math Help - Co-ordinates

1. Co-ordinates

The points A, B and C have Co-ordinates (5,1)(p,7)(8,2) respectively.

Given that AB is twice the distance of AC. Calculate the possible values of p.
Thanks!

2. $You\ have\ two\ solutions.$

$Calculate\ the\ length\ of\ AC\ using\ Pythagoras'\ theorem.$

$Then\ B\ lies\ on\ a\ circle\ of\ twice\ that\ radius.$

$The\ y\ co-ordinate\ of\ both\ points\ is\ 7.$

$Solve\ for\ the\ two\ values\ of\ x.$