Evaluating limit by factorization

In summary, the conversation discusses the factorization method for solving a limit problem and how it is useful for indeterminate forms. It also mentions a discrepancy in the answer given and the correct answer for the specific limit problem. The conversation ends with a clarification on the problem and a demonstration of the factorization method.
  • #1
Joel Jacon
11
0
Can anyone tell me how to solve the following limit by factorization method
$\lim{{x}\to{5}} \frac{x^3 + 3x^2 - 6x + 2}{ x^3 + 3x^2 - 3x - 1}$?Please tell me how to factorize such big equation?
 
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  • #2
Why do you want to factorize it?
The factorization method is useful when the limit is of an indeterminate form like $\frac{0}{0}$ or $\frac{\infty}{\infty}$. But this is not the case thus you can just plug in the value $x=5$.
 
  • #3
But the answer given in my book is -11. While using direct substitution I get 9. How can you get -11
 
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  • #4
$$\lim_{x\to5}\frac{x^3+3x^2-6x+2}{x^3+3x^2-3x-1}=\frac{172}{184}=\frac{43}{46}$$$$\text{ }$$Are you sure you typed the problem correctly?
 
  • #5
Yes, the question is correct. See the question 1 in the image
 

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  • #6
After saving the image, and rotating it so that it is not upside down, then straining my eyes to read the out of focus image, what I see is:

1.) \(\displaystyle \lim_{x\to5}\frac{2x^2+9x-5}{x+5}\)

Now, you can factor as follows (although it is not necessary):

\(\displaystyle \lim_{x\to5}\frac{(2x-1)(x+5)}{x+5}=\lim_{x\to5}2x-1=2(5)-1=9\)

Apparently what was meant, if an answer of $-11$ was given is:

\(\displaystyle \lim_{x\to-5}\frac{2x^2+9x-5}{x+5}=2(-5)-1=-11\)
 

FAQ: Evaluating limit by factorization

1. What is factorization?

Factorization is the process of breaking down a mathematical expression or number into its prime factors. This allows us to simplify and solve complex equations more easily.

2. Why is factorization important in evaluating limits?

Factorization is important in evaluating limits because it allows us to identify any common factors or cancel out terms in the numerator and denominator, making it easier to find the limit.

3. How do you factorize an expression?

To factorize an expression, we need to identify any common factors and use algebraic techniques such as factoring by grouping, difference of squares, or perfect square trinomials. We can also use the rational root theorem to find rational factors.

4. Can factorization be used for all limits?

No, factorization can only be used for limits that involve polynomials. If the limit involves trigonometric, exponential, or logarithmic functions, other methods such as L'Hopital's rule or substitution may need to be used.

5. Are there any limitations to using factorization in evaluating limits?

Yes, factorization may not always be possible or may be very time-consuming for complex expressions. In addition, it may not work for limits involving irrational or imaginary numbers. In these cases, other methods of evaluating limits may be more effective.

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