Question #35611

Question

914 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2017-07-18T04:54:58

#z^6=-64#

De Moivre's Theorem states that:

#z^n=(rcis(x))^n=r^ncis(nx)#

We will want to expand out the cis form to then convert to rectangular form:

#r^ncis(nx)=r^n(cos(nx)+isin(nx))#

Ok, now apply the theorem to the complex number:

#z^6=2^6cis(6*30˚)=64cis(180˚)=64(cos(180˚)+isin(180˚))#

From the unit circle:

#cos(180˚)=-1#

#sin(180˚)=0#

Therefore:

#64(cos(180˚)+isin(180˚))=64(-1+0i)=-64#

Interestingly, the imaginary component is zero.