Given polynomial is 3x2-x-4
we have,3x2-x-4=3x2+3x-x-4
=3x(x+) - (x+)
=(x+)(3x-)
the value of 3x2-x-4 is 0 when the value of(x+)(3x-)is 0.
when x+=0 or 3x-=0