Please help!
Which of the following is a third root of the given complex number?
27(cos(pi/5)+isin(pi/5))

check all that apply.
a. 27(cos(11pi/15)+isin(11pi/15))
b. 3(cos(pi/5)+isin(pi/15))
c. 3(cos(11pi/150+isin(11pi/15))
d. 3(cos(8pi/15)+isin(8pi/15))

Question

Please help!
Which of the following is a third root of the given complex number?
27(cos(pi/5)+isin(pi/5))

check all that apply.
a. 27(cos(11pi/15)+isin(11pi/15))
b. 3(cos(pi/5)+isin(pi/15))
c. 3(cos(11pi/150+isin(11pi/15))
d. 3(cos(8pi/15)+isin(8pi/15))

tkhunny · Answer

Discard a. immediately.  Wrong magnitude.
Discard b. immediately.  Wrong denominator unless you just typed it badly.

anonymous · Answer

oops! I did! b.'s denominators are both 15! @tkhunny could you please help me figure out how to do this problem?

tkhunny · Answer

Third Roots differ by 120º or $\dfrac{2\pi}{3}$

b. with the 15 is the first one.  Add the increment twice and you should have the other two.