Divide -2x^3+21x^2-20x-12 by (x-3)
Please explain.
You can try to set it up like long division (to check, multiply):
......-2x^2 + 15x + 25 R 63
...________________________
x-3)-2x^3 + 21x^2 - 20x - 12
....-2x^3 + 6x^2 -->subtracting will change signs
.....___________
............15x^2 - 20x
............15x^2 - 45x -->subtracting will change signs
............___________
....................25x - 12
....................25x - 75 -->subtracting will change signs
...................._________
......................... 63(remainder)