x4 + x3 + x2 + x + 1Let p(x) = x4 + x3 + x2 + x + 1The zero of x + 1 is - 1.p(- 1) = (- 1)4 + (- 1)3 + (- 1)2 + (- 1) + 1= 1 - 1 + 1 - 1 + 1 = 1 ≠ 0∴ By factor theorem, x + 1 is not a factor of x4 + x3 + x2 + x + 1.