Question

factor.
3x^2-5x-12

Answer 1

try to find those 2no. which has a product=3*12=36, and have a difference between them=5.
we have,
36=1*36
36=2*18
36=3*12
36=4*9 ----------->here, we have a difference of 5 between the no.(irrespective of signs)

\[3x^{2}-5x-12\]
\[3x^{2}-9x+4x-12\] (writing -5 as sum of -9 and 4)
Take out common value from any two groups
\[[3x^{2}-9x][+4x-12]\]

\[3x(x-3)3(+x-3)\]

=\[(3x+3)(x-3)\]