You can divide a factor of 2 from all terms:
2(10x² +3x -4)
You can look for factors of 10×(-4) = -40 that add to 3.
-40 = 40×-1 = 20×-2 = 10×-4 = 8×-5 . . . . . these last ones add to 3
Now, you know the factorization is
2(10x +8)(10x -5)/10 = 2(5x +4)(2x -1)
One factor of 20x² +6x -8 is any of
2
5x +4
2x -1
or any product of 2 of these.
