# Long Division

• Jan 19th 2007, 07:00 PM
symmetry
Long Division
Use long division to divide

x^3 − 8x^2 + x + 2 by x − 7.

Also, what is the difference between synthetic and long division?

Which of the two is best to play with?
• Jan 19th 2007, 09:03 PM
ticbol
Quote:

Originally Posted by symmetry
Use long division to divide

x^3 − 8x^2 + x + 2 by x − 7.

Also, what is the difference between synthetic and long division?

Which of the two is best to play with?

In long division, you divide the usual way. You subtract the whatsamacallit from the old dividend to get a new dividend.
In synthetic division, you "divide" "the reverse" way. You add the "whatsamacallit" with the old dividend to get a new dividend.

Also, in synthetic division, you deal with the numerical coefficients only, while in the long division, you deal with both numerical coefficients and the variables.

--------------------
(x^3 +3) / (x -2) == x^3 /x == x^2 first.
Then, (x^2) *(x -2) = x^3 -2x
That "x^3 -2x" is what I call whatsamacallit, because I don't know what am I going to call it.

-------------------------------
Which one is better to play with?
For me, the synthetic division, because it is "faster".

But I am more comfortable with the long division, because it is more reliable or I commit less or no mistakes in using that. And in long division, there is no guessing for the next, new divisor. No trial and error to get going.

----------------------------

x^3 − 8x^2 + x + 2 by x − 7.

a) (x-7) | x^3 -8x^2 +x +2 === x^3 /x === x^2 ----first quotient.

b) (x^2)*(x-7) = x^3 -7x^2 ------------------------whatsamacallit.

c) (x^3 -8x^2 +x +2) -(x^3 -7x^2) = -x^2 +x +2 ----new dividend.

d) (-x^2) / x === -x
So, new quotient is (x^2 -x)

e) (-x)*(x-7) = -x^2 +7x --------------------------whatsamacallit again.

f) (-x^2 +x +2) -(-x^2 +7x) = -6x +2 ---------------newer dividend.

g)(-6x) / x === -6
So, newer quotient is (x^2 -x -6)

h) (-6)*(x-7) = -6x +42 ----------------you're right, whatsamacallit again.

i) (-6x +2) -(-6x +42) = -40 -----------the remainder.

Therefore,
(x^3 -8x^2 +x +2) / (x-7) = x^2 -x -6, remainder (-40). -----answer.
• Jan 20th 2007, 01:11 AM
CaptainBlack
Quote:

Originally Posted by symmetry

Which of the two is best to play with?

Learn sysnthetic division because you have to for exams etc, remember that
it exists, then never use it again. In the big picture polynomial long division
is more general, and concentrating on it will result in one less thing to
remember.

RonL
• Jan 20th 2007, 05:39 AM
symmetry
ok
I thank you for the replies and for the tip given about learning synthetic division.