E(x) = (x² + x + 1)² – (x² + x)² – x²
= (x² + x + 1)² – (x² + x)² – x² – x + x
= (x² + x + 1)² – (x² + x)² – (x² + x) + x
= (x² + x + 1)² – (x² + x)[(x² + x) + 1) + x
= (x² + x + 1)² – (x² + x)(x² + x + 1) + x
= (x² + x + 1)[(x² + x + 1) – (x² + x)] + x
= (x² + x + 1)·1 + x
= x² + x + 1 + x
= x² + 2x + 1
= (x + 1)²