Math Problem Statement
Evaluate lim x→8 3 √x−2 x−8 .
Solution
We are tasked with evaluating the limit:
Direct substitution of results in an indeterminate form , so we must use algebraic techniques to simplify the expression. In this case, we can use the technique of rationalizing the numerator, as the cube root function is involved.
Step 1: Rewrite the expression
We need to simplify the given limit:
To rationalize, we multiply both the numerator and the denominator by the expression that will eliminate the cube root in the numerator. This is:
[ \frac{(\sqrt[3]{x} - 2)(\sqrt[3]{x^2} + 2\sqrt[3]{x} + 4)}{(x - 8)(\sqrt[3]{x^2} + 2\sqrt[3]{x} + 4)} ]
Step 2: Simplify using the identity
Using the identity , where and , we get:
[ (\sqrt[3]{x} - 2)(\sqrt[3]{x^2} + 2\sqrt[3]{x} + 4) = x - 8 ]
Thus, the expression becomes:
[ \frac{x - 8}{(x - 8)(\sqrt[3]{x^2} + 2\sqrt[3]{x} + 4)} = \frac{1}{\sqrt[3]{x^2} + 2\sqrt[3]{x} + 4} ]
Step 3: Evaluate the limit
Now, we substitute into the simplified expression:
[ \frac{1}{\sqrt[3]{8^2} + 2\sqrt[3]{8} + 4} = \frac{1}{\sqrt[3]{64} + 2 \cdot \sqrt[3]{8} + 4} ]
Since and , we have:
Final Answer:
Would you like further explanation or details on any step? Here are some related questions you can explore:
- How can you rationalize cube roots in other types of limits?
- What is the difference between using direct substitution versus rationalization in limits?
- How would this process change for a square root instead of a cube root?
- Can L'Hopital's Rule be used to solve this limit problem?
- What happens when you apply limits at infinity for similar rational expressions?
Tip: When dealing with indeterminate forms, rationalizing can be an effective tool for simplifying expressions, especially with roots.
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Math Problem Analysis
Mathematical Concepts
Limits
Indeterminate Forms
Rationalization
Cube Roots
Formulas
lim (x→a) f(x) / g(x) = 0/0 (Indeterminate Form)
(a - b)(a^2 + ab + b^2) = a^3 - b^3 (Rationalizing the numerator)
Theorems
Limit Theorem
Indeterminate Forms
Rationalization Techniques
Suitable Grade Level
Grades 11-12 (Advanced High School Calculus)
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