I think your question is
3x^2+2x-1
To factories this
Splitting the middle term can be used
That is
2x can be written as 3x-1x
3x^2+(3x-1x)-1
We can write
(3x^2+3x)-x-1
=3x(x+1)-1(x+1)
=(x+1)(3x-1)
it is the factor of this
If your question is 3x^2+2x+1
Then factorisation is much more difficult