Question

Factorise the following by taking out the common factors:
d) $12a^3+15a^{2}b–21a{b}^2$

Answer 1

Given: $12a^3+15a^{2}b–21a{b}^2$

The common factor is $3a$

Dividing by $3a$ in above expression, we get,

$\left\{\frac{12a^3}{3a}\right\}$+$\left\{\frac{15a^{2}b}{3a}\right\}$ –$\left\{\frac{21a{b}^2}{3a}\right\}$

$=4a^2+5ab–7b^2$

$\therefore 12a^3+15a^{2}b–21a{b}^2=3a(4a^2+5ab–7b^2)$.