Is the question wrong, or am I missing something?
Which expression is a cube root of -2i?
a. cube root 2 (cos(60) + isin(60))
b. cube root 2 (cos(90) + isin(90))
c. cube root 2 (cos(260) + isin(260))
d. cube root 2 (cos(210) + isin(210))

Question

Is the question wrong, or am I missing something? 
Which expression is a cube root of -2i?
a. cube root 2 (cos(60) + isin(60))
b. cube root 2 (cos(90) + isin(90))
c. cube root 2 (cos(260) + isin(260))
d. cube root 2 (cos(210) + isin(210))

anonymous · Answer

I'm getting that both b and d are correct answers, but the question only lets me choose one. http://www.wolframalpha.com/input/?i=cube+root+%28-2i%29 cube root -2i http://www.wolframalpha.com/input/?i=cube+root+2+%28cos+%2890%29%2Bi+sin+%2890%29%29 option b, which equals ~1.2599i, which is a root of -2i as listed in the first link http://www.wolframalpha.com/input/?i=cube+root+2+%28cos+%28210%29%2Bi+sin+%28210%29%29 option d, which equals ~ -1.091-0.62i, which also is a cube root. Did I enter something in wrong or is the question just inaccurate somehow? https://gyazo.com/51bca4b7256671f3d99e8fb0baba8f7e Picture of the choices.

baru · Answer

hmm...
i think you are right, both b and d seem to be correct

anonymous · Answer

It was D, apparently, but my instructor for this class is incompetent.