De Moivre's theorem proves to be most useful tool in solving the complex numbers involving higher powers and the complex numbers having powers in fractions. De Moivre's theorem is also helpful in finding the nth roots of a complex numbers.
De Moivre's theorem is used to find the powers and the roots of complex numbers. De Moivre's theorem is

(Cosx+iSinx)= Cosnx+iSinnx
The following are the steps to be carried out in De Moivres theorem.

Step -1 
Read the problem and list all the values given.
Step -2
Substitute the values in the corresponding formula to obtain the value.

(Cosx + iSinx)n = Cosnx + iSinnx