# polynomial

• Nov 24th 2008, 06:20 PM
Joker37
polynomial
The remainder when -4x^2 + 2x + 7 is divided by (x - c) is -5. Find a possible whole number value of c.
• Nov 24th 2008, 06:26 PM
Smancer
Well... why not divide and see what you get! Its too complicated for me to write out but I get x - c goes into -4x^2 +2x +7, -4x + (2-4c) times with a remainder of 7+(2 - 4c)*c

Can you figure it out from there?
• Nov 24th 2008, 06:40 PM
Joker37
Not really...I'd rather someone show me a complete worked out solution (I'd understand how to do this if the -c in x - c was a number). And be quick please everybody... the faster I get a response the more math I can do!

Sorry, if that seemed rude anyway, I'd appreciate any more responses.
• Nov 24th 2008, 07:01 PM
Joker37
Also, I don't think you need to divide -4x^2 + 2x + 7 by the x - c to find out the answer. I am looking for this other way.
• Nov 24th 2008, 07:02 PM
o_O
The remainder theorem says: If a polynomial $p(x)$ is divided by a linear factor $x - a$, then the remainder is equal to $p(a)$

So, we have the solve the equation: $p(a) = -5 \ \iff \ -4a^2+2a + 7 = -5$

Move -5 to the other side to get: $-4a^2 + 2a + 12 = 0$

This is a simple, factorable quadratic. See if you can go on from here.
• Nov 24th 2008, 09:37 PM
tyco3c
I don't understand.
• Nov 25th 2008, 03:32 AM
CaptainBlack
Quote:

Originally Posted by tyco3c
I don't understand.

Quote what you are refering to so that we know what help you need.

CB