I dont really know where to get start on this, all I can really figure out is:

a|b <=> b = a (d)

a^2|b^2 <=> b^2 = a^2 (d)

therefore there is some common d that is in a|b and a^2|b^2

I kinda doubt this is enough for a proof or if it really even proves anything really.

Can someone help me out here?