Math Problem Statement

If lim f(x) = 3 and lim g(x) = -4, find lim [ -2(g(x))^2 / (f(x) + 5) ]

Solution

We are given the following limits:

limxaf(x)=3andlimxag(x)=4,\lim_{{x \to a}} f(x) = 3 \quad \text{and} \quad \lim_{{x \to a}} g(x) = -4,

and we are asked to evaluate the limit:

limxa2[g(x)]2f(x)+5.\lim_{{x \to a}} \frac{-2[g(x)]^2}{f(x) + 5}.

Step-by-step Solution:

  1. Substitute the limit values of f(x)f(x) and g(x)g(x):

f(x)3andg(x)4asxa.f(x) \to 3 \quad \text{and} \quad g(x) \to -4 \quad \text{as} \quad x \to a.

  1. Evaluate the expression using these limit values:

[ \lim_{{x \to a}} \frac{-2[g(x)]^2}{f(x) + 5} = \frac{-2[-4]^2}{3 + 5}. ]

  1. Simplify the expression:
  • First, calculate [4]2[-4]^2: [4]2=16.[-4]^2 = 16.

  • Now, substitute back: 2(16)3+5=328.\frac{-2(16)}{3 + 5} = \frac{-32}{8}.

  1. Final simplification:

328=4.\frac{-32}{8} = -4.

Thus, the value of the limit is 4-4.

Answer:

The correct choice is A. 4-4.


Would you like more details or have any questions? Here are some related questions for further understanding:

  1. What is the general procedure for evaluating limits involving fractions?
  2. How do squared terms affect the outcome of limit problems?
  3. What happens if one of the functions f(x)f(x) or g(x)g(x) approaches 0?
  4. How would the limit change if the denominator approached 0?
  5. Can limits of composite functions always be computed by substitution?

Tip: When solving limit problems, always check if direct substitution simplifies the expression. If not, consider algebraic simplification or limit laws.

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Math Problem Analysis

Mathematical Concepts

Limits
Substitution in Limits
Simplification

Formulas

lim_{x→a} [g(x)]^2 = [lim_{x→a} g(x)]^2
Direct substitution in limits

Theorems

Limit of a function
Substitution theorem in limits

Suitable Grade Level

Grades 10-12