Multivariable Calculus, 7th Edition

$r=\frac{2}{cos\theta + sin \theta}$
Given: $x+y=2$ To convert this equation into polar form, we will substitute $x=rcos\theta$ and $y=rsin \theta$ Thus, $rcos\theta + rsin \theta =2$ or $r=\frac{2}{cos\theta + sin \theta}$