Question

factorises : 121x⁴ - 81x²​

Answer 1

$121 {x}^{4} - 81 {x}^{2} \\ = {(11 {x}^{2} )}^{2} - {(9x)}^{2} \\ = (11 {x}^{2} + 9x)(11 {x}^{2} - 9x) \\ (becoz \: {a}^{2} - {b}^{2} = (a + b)(a - b)) \\ = {x}^{2} (11x + 9)(11x - 9)$