From the point \((0, a)\) draw a straight line at an angle \(\varphi\) to the \(y\)-axis. Find the distribution function for the abscissa of the point of intersection of this line with the \(x\)-axis if

(a) the angle \(\varphi\) is uniformly distributed in the interval \(\left(0, \frac{\pi}{2}\right)\);

(b) the angle \(\varphi\) is uniformly distributed in the interval \(\left(-\frac{\pi}{2}, \frac{\pi}{2}\right)\).