81x3-x

Likely interpretation: 81x^3 − x

• Factor out x: x(81x^2 − 1)
• 81x^2 − 1 is a difference of squares: (9x)^2 − 1^2 = (9x − 1)(9x + 1)

So the factorization is: x(9x − 1)(9x + 1)

If you meant 81 × 3 − x instead, that’s 243 − x.

If you were solving 81x^3 − x = 0, the roots are x = 0, x = 1/9, x = −1/9.