Factorise : $3 x^{2}-x-4$
Factorise : $3 x^{2}-x-4$
$3 x^{2}-x-4$
We have $a =3$, $b =-1$ and $c =-4$
$\therefore l+ m =-1 $ and $lm =3 \times(-4)=-12$
$\therefore $ $ l=-4$ and $m =3 $
Now, $3 x ^{2}- x -4=3 x ^{2}-4 x +3 x -4$
$=x(3 x-4)+1(3 x-4)=(3 x-4)(x+1)$
Thus, $3 x^{2}-x-4=(3 x-4)(x+1)$
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