Solution:
we have
Putting x = 1, -1, i and -i respectively, we get
Adding (i) and (ii), we get
Adding (iii) and (iv), we get
Adding (v) and (vi), we get
If , then the value of is
we have
Putting x = 1, -1, i and -i respectively, we get
Adding (i) and (ii), we get
Adding (iii) and (iv), we get
Adding (v) and (vi), we get