mycroft holmes
Last Activity: 8 Years ago
Write the equation as (x+1)3 = -2. Then the roots are (-2)1/3-1, (-2)1/3w-1, and (-2)1/3w2 – 1, where w is the primitive cube root of unity.
Then sum of non-real roots = [ (-2)1/3w-1]+ [ (-2)1/3w2 – 1] = -[ (2)1/3w +(2)1/3w2] -2 = 21/3 - 2 [Since 1+w+w2= 0]
= -[2-21/3]. 2>21/3 >1. Hence 1>2-21/3>0 and hence -11/3 - 2
Hence the option C is correct