Factorise x⁴ − 81.

(x² + 9)(x + 3)(x − 3)

No citable source has been recorded for this record. Treat it as practice material, not as fact.

Explanation

It is a difference of squares twice over: x⁴ − 81 = (x² + 9)(x² − 9) and x² − 9 = (x + 3)(x − 3).