Math Problem Statement

Find the limit as x approaches 2 of (3x^2 - 8x + 4) / (5x^2 - 14x + 8).

Solution

We are asked to find the limit:

limx23x28x+45x214x+8\lim_{x \to 2} \frac{3x^2 - 8x + 4}{5x^2 - 14x + 8}

Step 1: Direct Substitution

First, substitute x=2x = 2 into both the numerator and the denominator to see if the limit can be evaluated directly.

For the numerator: 3(2)28(2)+4=3(4)16+4=1216+4=03(2)^2 - 8(2) + 4 = 3(4) - 16 + 4 = 12 - 16 + 4 = 0

For the denominator: 5(2)214(2)+8=5(4)28+8=2028+8=05(2)^2 - 14(2) + 8 = 5(4) - 28 + 8 = 20 - 28 + 8 = 0

Since both the numerator and denominator are zero when x=2x = 2, we have an indeterminate form 00\frac{0}{0}, so we need to apply factoring or L'Hôpital's Rule.

Step 2: Factoring the expression

Let's factor both the numerator and the denominator.

The numerator 3x28x+43x^2 - 8x + 4 can be factored as: 3x28x+4=(3x2)(x2)3x^2 - 8x + 4 = (3x - 2)(x - 2)

The denominator 5x214x+85x^2 - 14x + 8 can be factored as: 5x214x+8=(5x4)(x2)5x^2 - 14x + 8 = (5x - 4)(x - 2)

Now the limit expression becomes: limx2(3x2)(x2)(5x4)(x2)\lim_{x \to 2} \frac{(3x - 2)(x - 2)}{(5x - 4)(x - 2)}

Step 3: Canceling common terms

Since (x2)(x - 2) is common in both the numerator and denominator, we cancel it out (note that x2x \neq 2, so this cancellation is valid): limx23x25x4\lim_{x \to 2} \frac{3x - 2}{5x - 4}

Step 4: Substituting x=2x = 2

Now substitute x=2x = 2 into the simplified expression: 3(2)25(2)4=62104=46=23\frac{3(2) - 2}{5(2) - 4} = \frac{6 - 2}{10 - 4} = \frac{4}{6} = \frac{2}{3}

Final Answer:

limx23x28x+45x214x+8=23\lim_{x \to 2} \frac{3x^2 - 8x + 4}{5x^2 - 14x + 8} = \frac{2}{3}

Let me know if you'd like more details or have any questions.

Here are some related questions to practice:

  1. What would happen if you tried to apply L'Hôpital's Rule instead of factoring?
  2. How can you find the limit if the numerator and denominator were both linear polynomials?
  3. What is the geometric interpretation of a limit that gives a fraction like 23\frac{2}{3}?
  4. How can factoring help in limits when the indeterminate form 00\frac{0}{0} occurs?
  5. What is the limit of x24x2\frac{x^2 - 4}{x - 2} as x2x \to 2?

Tip: Always check if a limit results in an indeterminate form before deciding on the method (factoring, L'Hôpital's Rule, etc.).

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Math Problem Analysis

Mathematical Concepts

Limits
Factoring
Indeterminate Form
Quadratic Equations

Formulas

Direct Substitution in Limits
Factoring Polynomials
Limit of Rational Functions

Theorems

L'Hôpital's Rule
Factorization Theorem

Suitable Grade Level

Grades 10-12