Math Problem Statement

Use direct substitution to obtain an undefined expression. Then, use the method of evaluating a limit of the form

K/0, K ≠ 0

to simplify the function to help determine the limit.

lim x→1+

2x2 − 5x − 3

x2 + x − 2

Solution

Let's solve the limit problem step-by-step.

Problem:

We are tasked with finding the limit of the function as x1+x \to 1^+ for the following:

limx1+2x25x3x2+x2\lim_{x \to 1^+} \frac{2x^2 - 5x - 3}{x^2 + x - 2}

Step 1: Direct Substitution

We'll first substitute x=1x = 1 into the function directly to check if we get an undefined expression:

Numerator:2(1)25(1)3=253=6\text{Numerator:} \quad 2(1)^2 - 5(1) - 3 = 2 - 5 - 3 = -6

Denominator:(1)2+(1)2=1+12=0\text{Denominator:} \quad (1)^2 + (1) - 2 = 1 + 1 - 2 = 0

The denominator equals 0, so we have the indeterminate form 60\frac{-6}{0}. Since the numerator is non-zero, we have an undefined expression at x=1x = 1, and this is a limit of the form K0\frac{K}{0} where K0K \neq 0. In such cases, we need to analyze the behavior of the function near x=1x = 1 to determine the limit.

Step 2: Factorize the Function

To simplify the expression, we'll factor both the numerator and the denominator.

Numerator:

The numerator is 2x25x32x^2 - 5x - 3. We need to factor this quadratic expression:

2x25x3=(2x+1)(x3)2x^2 - 5x - 3 = (2x + 1)(x - 3)

Denominator:

The denominator is x2+x2x^2 + x - 2, which can also be factored:

x2+x2=(x1)(x+2)x^2 + x - 2 = (x - 1)(x + 2)

Now, we can rewrite the original expression as:

2x25x3x2+x2=(2x+1)(x3)(x1)(x+2)\frac{2x^2 - 5x - 3}{x^2 + x - 2} = \frac{(2x + 1)(x - 3)}{(x - 1)(x + 2)}

Step 3: Analyze the Limit as x1+x \to 1^+

At this point, we can analyze the behavior of the function as xx approaches 1 from the right.

Substitute x=1x = 1 into the factored form:

Numerator:(2(1)+1)(13)=(2+1)(2)=3(2)=6\text{Numerator:} \quad (2(1) + 1)(1 - 3) = (2 + 1)(-2) = 3(-2) = -6

Denominator:(11)(1+2)=(0)(3)=0\text{Denominator:} \quad (1 - 1)(1 + 2) = (0)(3) = 0

Since the denominator tends to 0 and the numerator remains non-zero, the limit will approach ±\pm \infty. To determine the exact behavior, we need to consider the sign of the denominator as x1+x \to 1^+.

As x1+x \to 1^+, the denominator:

(x - 1) \to 0^+ \quad \text{(positive side, since x \to 1^+)}

Thus, the denominator approaches 0 from the positive side. The numerator remains negative (6-6), and so the limit will be:

limx1+(2x+1)(x3)(x1)(x+2)=\lim_{x \to 1^+} \frac{(2x + 1)(x - 3)}{(x - 1)(x + 2)} = -\infty

Final Answer:

limx1+2x25x3x2+x2=\lim_{x \to 1^+} \frac{2x^2 - 5x - 3}{x^2 + x - 2} = -\infty


Would you like any further clarification or additional steps? Here are some follow-up questions:

  1. How do we factor quadratic expressions efficiently?
  2. What does it mean for a limit to approach ±\pm \infty?
  3. Can limits of the form K0\frac{K}{0} have finite values?
  4. What happens if both the numerator and denominator tend to zero (indeterminate form 0/00/0)?
  5. How does the behavior of the function change when we approach from the left, x1x \to 1^-?

Tip: When you encounter indeterminate forms like K0\frac{K}{0}, always analyze the sign of the denominator near the point to determine if the limit tends to ++\infty or -\infty.

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Math Problem Analysis

Mathematical Concepts

Limits
Indeterminate Forms
Factorization
Rational Functions

Formulas

lim x→a (f(x)) = L
Factoring quadratic expressions

Theorems

Limit of a rational function
Indeterminate forms of type K/0 (K ≠ 0)

Suitable Grade Level

Grades 11-12