Answer
$y = (tan\theta) x - a \tan\theta $
$m = \tan\theta$ and $c=-a\tan\theta$
Work Step by Step
Slope - intercept form of a straight line can be given by equation $y=mx+c$.
$y =(x-a) \times tan\theta = (tan\theta) x - a \tan\theta$
By putting point (x, y) (a, 0), we will see that LHS=RH, hence function y passes through (a, 0).