Question

factorise completely x^4-81​

Answer 1

= (x^2)^2 - (9)^2

= (x^2 - 9)(x^2 + 9).

Answer 2

x4-81

x4-81(x²)² - (9)²

x4-81(x²)² - (9)²(x² - 9)(x²+9)

x4-81(x²)² - (9)²(x² - 9)(x²+9)((x)²-(3)²)(x²+9)

x4-81(x²)² - (9)²(x² - 9)(x²+9)((x)²-(3)²)(x²+9)(x-3)(x+3)(x²+9)