(b)We have
$max\ amp(z)=amp$$({z_2}),$ $min\ amp (z)=amp$$({z_1})$
Now $amp({z_1}) = {\theta _1} = {\cos ^{ – 1}}\left( {\frac{{15}}{{25}}} \right) = {\cos ^{ – 1}}\left( {\frac{3}{5}} \right)$
$amp({z_2}) = \frac{\pi }{2} + {\theta _2} = \frac{\pi }{2} + {\sin ^{ – 1}}\left( {\frac{{15}}{{25}}} \right) = \frac{\pi }{2} + {\sin ^{ – 1}}\left( {\frac{3}{5}} \right)$
$|\max \,\,amp(z) – \min \,\,amp(z)|$
$ = \left| {\frac{\pi }{2} + {{\sin }^{ – 1}}\frac{3}{5} – {{\cos }^{ – 1}}\frac{3}{5}} \right|$
$ = \left| {\frac{\pi }{2} + \frac{\pi }{2} – {{\cos }^{ – 1}}\frac{3}{5} – {{\cos }^{ – 1}}\frac{3}{5}} \right| = \pi – 2{\cos ^{ – 1}}\frac{3}{5}$