Remainder Theorem: Solve x^80 - 8x^30 + 9x^24 + 5x + 6 Divided by (x+1)

In summary, the remainder theorem states that if p(x) / (x – a) = q(x) with remainder r(x), then p(x) = (x – a) q(x) + r(x). So if x=-1, then r=3.
  • #1
duki
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0

Homework Statement



Find the remainder when (x^80 - 8x^30 + 9x^24 + 5x + 6) is divided by (x+1)

Homework Equations



The Attempt at a Solution



So I'm not really sure where to start. I tried starting by doing long polynomial division, but I get stuck. How do I start this?
 
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  • #2
What does the remainder theorem say?
 
  • #3
Yeah, you would get stuck doing the division. It's a long haul. But look, suppose you did do the division f(x)=(x^80 - 8x^30 + 9x^24 + 5x + 6) by (x+1)? Then you would get f(x)=q(x)*(x+1)+r, right? Where q(x) is the quotient and r is the remainder. What happens if you put x=(-1) into that?
 
  • #4
Remainder Theorem:
If p(x) / (x – a) = q(x) with remainder r(x),

then p(x) = (x – a) q(x) + r(x).
 
  • #5
Dick said:
Yeah, you would get stuck doing the division. It's a long haul. But look, suppose you did do the division f(x)=(x^80 - 8x^30 + 9x^24 + 5x + 6) by (x+1)? Then you would get f(x)=q(x)*(x+1)+r, right? Where q(x) is the quotient and r is the remainder. What happens if you put x=(-1) into that?

You get r ?
 
  • #6
Well, yes. You get f(-1)=r. That's the remainder theorem. So what is r?
 
  • #7
Do you get:

(1 - 8 + 9 -5 + 6) = 3 ? So r = 3?
 
  • #8
Sure. If you don't believe it make up a simpler example where you can actually do the long division and check that it works. It's good for you.
 
  • #9
Thanks. How did you know to use -1?
 
  • #10
duki said:
Thanks. How did you know to use -1?

Look back at the problem. I'll give you three guesses. The first one had better be right.
 
  • #11
Because a = x + 1, so x = -1?
 
  • #12
What's a? If a=x+1 then x=a-1. You are onto the second guess.
 
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  • #13
Dick said:
What's a? If a=x+1 then x=a-1. You are onto the second guess.

Well heck, I'm not sure. :O
I assume we're using -1 because of something to do with (x+1) = 0 or something?
 
  • #14
Yes, if you had spent all day figuring out the q(x) in f(x)=q(x)*(x+1)+r by doing the horrible division, at the end of it all you could realize that you didn't need to find q(x) at all because if you put x=(-1) the q(x) disappears. That's the remainder theorem.
 
  • #15
Sweets.
So if for example I was dividing by (x-4), I would use 4 instead of -1?
 
  • #16
f(x)=q(x)*(x-4)+r. Sure, f(4)=r. You don't need to find q(x) before you know the remainder.
 
  • #17
How cool is that.
 
  • #18
Way cool.
 

FAQ: Remainder Theorem: Solve x^80 - 8x^30 + 9x^24 + 5x + 6 Divided by (x+1)

What is the Remainder Theorem?

The Remainder Theorem states that when a polynomial function is divided by a linear factor, the remainder is equal to the value of the function at the root of the linear factor. In other words, if we divide a polynomial f(x) by (x-a), the remainder will be equal to f(a).

How do I use the Remainder Theorem to solve a polynomial division problem?

To use the Remainder Theorem, first identify the linear factor that the polynomial is being divided by. Then, plug the value of this factor into the original polynomial to find the remainder. This remainder will be the value of the function at the root of the linear factor.

What is the purpose of dividing a polynomial by a linear factor?

Dividing a polynomial by a linear factor can help us simplify complex polynomial expressions and identify important characteristics of the function, such as its roots and end behavior.

How do I apply the Remainder Theorem to the given polynomial, x^80 - 8x^30 + 9x^24 + 5x + 6 Divided by (x+1)?

To apply the Remainder Theorem to this polynomial, we first need to identify the linear factor, which is (x+1). Then, we can substitute -1 (the root of the linear factor) into the polynomial to find the remainder. In this case, the remainder will be -9.

Can the Remainder Theorem be used for any polynomial division problem?

Yes, the Remainder Theorem can be used for any polynomial division problem as long as the divisor is a linear factor. However, it is important to note that the remainder will only be accurate if the polynomial is divided by its simplest form (all terms are in descending order and all exponents are present).

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