Question

Factorise the following by taking out the common factors:
12a³ + 15a²b - 21ab²

Answer 1

12a³ + 15a²b - 21ab²
Here, the common factor is 3a.
Dividing throughout by 3a, we get

`(12"a"^3)/(3"a") + (15"a"^2"b")/(3"a") - (21"ab"^2)/(3"a")`
= 4a² + 5ab - 7b²
∴ 12a³ + 15a²b - 21ab²
= 3a(4a² + 5ab - 7b²).