How do you convert y = x into polar form?

I found: ##tan(theta)=1##
Consider the following diagram:

We can see that the relationships between rectangular and are:
##r=sqrt(x^2+y^2)##
##theta=arctan(y/x)##
and:
##x=rcos(theta)##
##y=rsin(theta)##
Given our expression:
##y=x##
you have:
##cancel(r)sin(theta)=cancel(r)cos(theta)##
and write:
##tan(theta)=1##