Simplifying a rational expression

Click For Summary

Discussion Overview

The discussion revolves around simplifying the rational expression (12+r-r^2)/(r^3 +3r^2). Participants explore various methods of factoring and simplifying the expression, including the identification of roots and the cancellation of common factors.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant expresses difficulty in simplifying the expression and proposes that the answer is (4-r)/r^2, mentioning the expansion of the numerator as (-r+4)(r+3).
  • Another participant provides a detailed solution, including the quadratic formula to find roots, and arrives at the same simplified expression (4-r)/r^2, while showing the steps of factoring both the numerator and denominator.
  • A third participant suggests an alternative factorization of the numerator as (3+r)(4-r) and the denominator as r^2(r+3), leading to the same simplified result after cancellation.
  • One participant notes the condition that r cannot equal -3 when canceling the common factor (r+3).

Areas of Agreement / Disagreement

Participants generally agree on the final simplified form of the expression as (4-r)/r^2, but there are multiple approaches and methods presented for reaching that conclusion. The discussion includes different factorization techniques and the implications of canceling terms.

Contextual Notes

There are assumptions regarding the values of r, particularly the restriction that r cannot equal -3 due to the cancellation of the factor (r+3). Additionally, the discussion does not resolve any potential misunderstandings about the factoring process or the implications of the quadratic formula used.

hollywalker
Messages
1
Reaction score
0
Hello,
I am having difficulty solving my math problems.

Simplify the expression:
(12+r-r^2)/(r^3 +3r^2)

The answer is (4-r)/r^2

I know that i can expand 12+r-r^2 as (-r+4)(r+3)
But i cannot figure out the rest. Please help me. Thanks
 
Mathematics news on Phys.org
hollywalker said:
Hello,
I am having difficulty solving my math problems.

Simplify the expression:
(12+r-r^2)/(r^3 +3r^2)

The answer is (4-r)/r^2

I know that i can expand 12+r-r^2 as (-r+4)(r+3)
But i cannot figure out the rest. Please help me. Thanks

(Wave)

$$-r^2+r+12=0$$

$$\Delta=b^2-4ac=1-4 (-1 \cdot 12)=1+48=49$$

$$r_{1,2}=\frac{-b \pm \sqrt{\Delta}}{2a}=\frac{-1 \pm 7}{-2}=4,-3$$

So,the expression can be written like that:

$$\frac{12+r-r^2}{r^3+3r^2}=\frac{-(r-4) \cdot (r+3)}{r^2 \cdot (r+3)}=\frac{-(r-4)}{r^2}=\frac{4-r}{r^2}$$
 
Hello, hollywalker!

Simplify: .\frac{12+r-r^2}{r^3 +3r^2}
Factor the numerator: 12+r-r^2 \:=\: (3+r)(4-r)
Factor the denominator: r^3 + 3r^2 \:=\:r^2(r+3)

The fraction becomes: .\frac{(3+r)(4-r)}{r^2(r+3)}

Reduce: .\frac{\cancel{(3+r)}(4-r)}{r^2\cancel{(r+3)}} \;=\;\frac{4-r}{r^2}
 
Also note that if you're crossing $(r+3)$ from the top and bottom, then $r \ne -3$.
 
Hi hollywalker, welcome to MHB!:)

I have moved your topic to a more appropriate sub-forum, and given a new title to it to indicate the nature of the question being asked.
 

Similar threads

  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 4 ·
Replies
4
Views
1K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 13 ·
Replies
13
Views
2K
Replies
3
Views
1K
Replies
1
Views
2K