Hello,

You should know the formula for a distance between 2 points :

M(a,b) N(c,d)

Then

Then for example

Square the equality PA=2PB it's far easier to work on this than the square roots that PA and PB represent.ii) suppose that P moves such that PA=2PB. Deduce that P moves on a circle

if you can't find the solution, tell me what you've done and we'll work it out ^^

Equation of a circle, of radius R and center O(m,n) :iii) Hence find the center and radius of this circle