# subtracting polynomials

• Mar 25th 2008, 11:47 AM
subtracting polynomials
7x+1 - x^2+3x-8
i got x^2-4x+9 but my teacher said it was wronge. how do I correctly solve this problem?
• Mar 25th 2008, 12:06 PM
Moo
Hello,

Where did the - go for x² ?
• Mar 25th 2008, 12:28 PM
I am not sure why would the x^2 be negative i am so lost
• Mar 25th 2008, 12:41 PM
mathceleb
Quote:

I am not sure why would the x^2 be negative i am so lost

Are you subtracting the entire last 3 terms? If not, the original expression you entered was:

$7x + 1 - x^2 + 3x - 8$

Grouping like terms and evaluating, we get:

$(7 + 3)x + (1 - 8) - x^2$
$10x -7 - x^2$

Rearranging this into proper form, we get:
$-x^2 + 10x -7$

Does that make sense?
• Mar 25th 2008, 12:45 PM
there where only 2 polnomials 7x+1 minus x^2+3x-8
• Mar 25th 2008, 12:47 PM
mathceleb
Quote:

there where only 2 polnomials 7x+1 minus x^2+3x-8

ok, then you should have written it like this:

$7x + 1 - (x^2 + 3x - 8)$

Now, distribute the negative sign for the second polynomial:

$7x + 1 - x^2 - 3x + 8$

Now group like terms:
$(7 - 3)x + (1 + 8) - x^2$
$-x^2 + 4x + 9$
• Mar 25th 2008, 01:05 PM