Question

Factorise:

$a^4-343a$

Answer 1

$Weknow{a}^3-b^3=(a-b)(a^2+ab+b^2)a^4-343a=a(a^3-343)=a(a^3-7^3)=a\left[\right(a-7\left)\right(a^2+7a+7^2\left)\right]=a\left[\right(a-7\left)\right(a^2+7a+49\left)\right]=a(a-7)(a^2+7a+49)$