$\left| {{z_1} + {z_2}} \right| \le \left| {{z_1}} \right| + \left| {{z_2}} \right|$

$\left| {{z_1} + {z_2}} \right| = \left| {{z_1}} \right| + \left| {{z_2}} \right|$

$\left| {{z_1} + {z_2}} \right| \ge \left| {{z_1}} \right| + \left| {{z_2}} \right|$

$\left| {{z_1} + {z_2}} \right| = \left| {{z_1}} \right| + \left| {{z_2}} \right| + \left| {{z_1} - {z_2}} \right|$