COMEDK2018MathematicsComplex Number
The maximum value of n < 101 , such that 1+ _ k-1 ^ n i^ k =0 is
Options
- A96
- B97
- C99
- D100
Correct answer
C. 99
Step-by-step solution
We have, _ n=1 ^ n i^ k =i+i²+i³+i⁴+i⁵+i⁶+i⁷+i⁸+i⁹+ Now as, i⁴=i⁸=i¹²= i^ n =1 and i+i²+i³+i⁴=0 So, _ n=1 ^ n i^ k =i+i²+i³+i⁴+i+i⁶+ i⁷+i⁸+i²+ aligned &=i+i²+i³+i⁴+ (i+i²+i³+i⁴ )+ (i+i²+i³+i⁴ )+ &=0+0+0+ aligned When we take n=99 after 96 th term, we will be left with 0+i+i²+i³=-1 So , for 1+ _ k=1 ^ n i^ k =0