Math Problem Statement

Evaluate the following limits: 1. lim(x→5) [2 / (x - 5)^6] 2. lim(x→3) [2 / (x - 3)] 3. lim(x→0) [1 / (x^2(x + 7))] 4. lim(x→-7) [1 / (x^2(x + 7))]

Solution

Let’s evaluate each limit step by step.


1. limx52(x5)6\lim_{x \to 5} \frac{2}{(x - 5)^6}
At x=5x = 5, the denominator becomes (55)6=06=0(5 - 5)^6 = 0^6 = 0. This makes the fraction undefined.
To determine the behavior near x=5x = 5:

  • When xx approaches 5 from the right (x5+x \to 5^+), (x5)6>0(x - 5)^6 > 0. Since 2/(x5)6>02/(x - 5)^6 > 0, the limit approaches ++\infty.
  • When xx approaches 5 from the left (x5x \to 5^-), (x5)6>0(x - 5)^6 > 0 (because n=6n = 6 is even). The value still approaches ++\infty.

Thus:
limx52(x5)6=\lim_{x \to 5} \frac{2}{(x - 5)^6} = \infty


2. limx32x3\lim_{x \to 3} \frac{2}{x - 3}
Here, the denominator becomes x3=0x - 3 = 0 at x=3x = 3. Again, we analyze the behavior near x=3x = 3:

  • When x3+x \to 3^+, x3>0x - 3 > 0. Hence 2x3+\frac{2}{x - 3} \to +\infty.
  • When x3x \to 3^-, x3<0x - 3 < 0. Hence 2x3\frac{2}{x - 3} \to -\infty.

Since the left- and right-hand limits are not the same, the limit does not exist.


3. limx01x2(x+7)\lim_{x \to 0} \frac{1}{x^2(x + 7)}
At x=0x = 0, the denominator becomes x2(x+7)=0x^2(x + 7) = 0. Analyzing the behavior:

  • x2>0x^2 > 0 for all x0x \neq 0, and x+7>0x + 7 > 0 for all xx near 0.
  • Thus, the denominator approaches 0+0^+, making 1x2(x+7)+\frac{1}{x^2(x + 7)} \to +\infty.

Therefore:
limx01x2(x+7)=\lim_{x \to 0} \frac{1}{x^2(x + 7)} = \infty


4. limx71x2(x+7)\lim_{x \to -7} \frac{1}{x^2(x + 7)}
At x=7x = -7, the denominator becomes x2(x+7)=(7)2(7+7)=49(0)=0x^2(x + 7) = (-7)^2(-7 + 7) = 49(0) = 0.
Near x=7x = -7, consider the sign of x+7x + 7:

  • When x7+x \to -7^+, x+7>0x + 7 > 0, so the denominator is x2(x+7)>0x^2(x + 7) > 0. Thus, 1x2(x+7)+\frac{1}{x^2(x + 7)} \to +\infty.
  • When x7x \to -7^-, x+7<0x + 7 < 0, so the denominator is x2(x+7)<0x^2(x + 7) < 0. Thus, 1x2(x+7)\frac{1}{x^2(x + 7)} \to -\infty.

Since the left- and right-hand limits are not the same, the limit does not exist.


Final Answers:

  1. \infty
  2. Does not exist
  3. \infty
  4. Does not exist

Would you like further clarifications or detailed steps for any part of the solution?


Related Questions:

  1. What does it mean for a limit to approach infinity, and how is it interpreted in graphs?
  2. How do we determine one-sided limits for rational functions with vertical asymptotes?
  3. Why does an even exponent in the denominator (e.g., (x5)6(x - 5)^6) affect the sign of the limit?
  4. What happens to limits if the numerator and denominator both approach zero (indeterminate forms)?
  5. How can limits involving infinity help us describe the behavior of functions at their vertical asymptotes?

Tip:

When analyzing limits with denominators approaching zero, always check the sign of the denominator near the critical point to determine the direction of the behavior (positive or negative infinity).

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Math Problem Analysis

Mathematical Concepts

Limits
One-sided limits
Behavior near vertical asymptotes
Infinity in limits

Formulas

Limit evaluation for rational functions
One-sided limit rules

Theorems

Limit Theorem
Infinity behavior theorem for rational functions with vertical asymptotes

Suitable Grade Level

Grades 11-12 (Advanced Precalculus or Calculus)