The above equation can be written as,
⇒(x31−x−31)[(x31)2+x31.x−31+(x−31)2)
We know that,
a3 - b3 = (a - b)(a2 + ab + b2)
∴(x31−x−31)[(x31)2+x31.x−31+(x−31)2]=(x31)3−(x−31)3⇒(x3×31)−(x3×−31)⇒x1−x−1⇒x−x1.
Hence, (x31−x−31)(x32+1+x−32)=x−x1.