Question 936570
<pre>

The polar substitutions are:

{{{x/r=cos(theta)}}} -> {{{x=r*cos(theta)}}}
{{{y/r=sin(theta)}}} -> {{{y=r*sin(theta)}}}
{{{r^2=x^2+y^2}}}    -> {{{r=sqrt(x^2+y^2)}}}

{{{y=x}}}
{{{r*sin(theta)=r*cos(theta)}}}
divide both sides by {{{r*cos(theta)}}}
{{{sin(theta)/cos(theta)=1}}}
{{{tan(theta)=1}}}
{{{theta=pi/4}}}

Edwin</pre>