Hello, moeyfrompunchy!
Did you even bother to make a sketch?
Find the equation of the locus of a point $\displaystyle P(x,y)$
that moves so that it is equidistant from the $\displaystyle x$axis and the $\displaystyle y$axis. Code:
 P
B +     *(x,y)
 x :
 :
 : y
 :
 :
++
 A

The point is $\displaystyle P(x,y).$
Its distance from the $\displaystyle x$axis is: .$\displaystyle PA = y.$
Its distance from the $\displaystyle y$axis is: .$\displaystyle PB = x.$
We want these distances to be equal: .$\displaystyle y \:=\:x$
How hard was that?