When you divide the polynomial 3x^2 + 7x - 20 by x + 4 using long division, you get:

Question

A: 3x^2 - 5

B: 3x + 19, R 46

C: 3x + 5

D: 3x - 5

E: 3x - 3, R -24

Answer 1

There is no symbol in the character set for this page that resembles the Long Division symbol, so let me use | instead

.         ______________
(x+4) | 3x^2 + 7x -20

When end using long division of polynomials only worry about the leading coefficient in each step. What do you have to do to x to eliminate a 3x^2 term? Obviously, you multiply by 3x.

 

......... ________3x_____
(x+4) | 3x^2 + 7x -20
. ..........3x^2 + 12x
. .....................________
...................... -5x -20

To eliminate -5x with an x term, you must multiply by -5

..........________3x_- 5____
(x+4) | 3x^2 + 7x -20
............3x^2 + 12x
..................... ________
...................... -5x - 20
...................... -5x - 20
....................... _______
............................... 0

 

so, the answer is 3x - 5

 

you can confirm the answer by multiplying (x + 4)(3x - 5) which gives

3x^2 -5x + 12x - 20 = 3x^2 + 7x - 20