I'm not too sure what I should've put as the title...

My teacher presented the class with a question that any of us has yet to solve.

Show that the plane that passes through the axis at $\displaystyle x=a$ , $\displaystyle y=b$ , $\displaystyle z=c$ and is described by the equation,

$\displaystyle (x/a)+(y/b)+(z/c)=1$

I have absolutely no idea how to approach this question and would appreciate any suggestions.