A question I'm stuck on, I'm never quite sure how to start off questions that require you to 'prove' things ... I don't have a very mathematical brain I think! :/ so here it is:

if p is the length if the perpendicular from the origin to the line x/a + y/b = 1, prove that 1/p² = 1/a² + 1/b².

I assume I'll have to use the perpendicular distance formula somehow, but I don't really know what to do ...