Chapter 10 - Section 10.3 - Polar Coordinates - 10.3 Exercises - Page 666: 16

$x=4$ This is a straight line with $x$-intercept 4.

$r=4sec\theta$ Since, $sec\theta=\frac{1}{cos \theta}$ $rcos \theta=4sec\theta\times cos \theta$ $rcos \theta=4$ To convert polar equation to Cartesian coordinates, we use the equations $rcos \theta=x$ and $rsin \theta=y$ Thus, $x=4$ This is a straight line with $x$-intercept 4.