5cis120 degrees
Find the 3rd root

Finding roots for problems like this is really quite simple -- just remember that . So here you have R = 5, = 120 ,and n = 1/3. Also keep in mind that the angle can also be written as + 360, + 720, etc. so in finding the nth root you will have multiple answers each varying by 360/n degrees from each other. Once you find one root, the other two can be found by adding multiples of 120 degrees. Can you take it from here?