We are asked to find the limit: $lim_{x \to 2} \frac{x^3 - 8}{\sqrt{x+2} - 2}$.

AnalysisLimitsCalculusRationalizationIndeterminate Forms
2025/5/5

1. Problem Description

We are asked to find the limit:
limx2x38x+22lim_{x \to 2} \frac{x^3 - 8}{\sqrt{x+2} - 2}.

2. Solution Steps

First, we note that if we directly substitute x=2x=2 into the expression, we get 2382+22=8842=00\frac{2^3 - 8}{\sqrt{2+2} - 2} = \frac{8-8}{\sqrt{4} - 2} = \frac{0}{0}, which is an indeterminate form.
We can factor the numerator using the difference of cubes formula:
a3b3=(ab)(a2+ab+b2)a^3 - b^3 = (a-b)(a^2 + ab + b^2).
So, x38=x323=(x2)(x2+2x+4)x^3 - 8 = x^3 - 2^3 = (x-2)(x^2 + 2x + 4).
Next, we can rationalize the denominator by multiplying the numerator and denominator by the conjugate of the denominator, which is x+2+2\sqrt{x+2} + 2:
x38x+22=(x2)(x2+2x+4)x+22x+2+2x+2+2=(x2)(x2+2x+4)(x+2+2)(x+2)222=(x2)(x2+2x+4)(x+2+2)x+24=(x2)(x2+2x+4)(x+2+2)x2\frac{x^3 - 8}{\sqrt{x+2} - 2} = \frac{(x-2)(x^2 + 2x + 4)}{\sqrt{x+2} - 2} \cdot \frac{\sqrt{x+2} + 2}{\sqrt{x+2} + 2} = \frac{(x-2)(x^2 + 2x + 4)(\sqrt{x+2} + 2)}{(\sqrt{x+2})^2 - 2^2} = \frac{(x-2)(x^2 + 2x + 4)(\sqrt{x+2} + 2)}{x+2 - 4} = \frac{(x-2)(x^2 + 2x + 4)(\sqrt{x+2} + 2)}{x-2}.
Now, we can cancel the (x2)(x-2) term in the numerator and denominator, since we are taking the limit as xx approaches 2, not when xx is equal to
2.
(x2)(x2+2x+4)(x+2+2)x2=(x2+2x+4)(x+2+2)\frac{(x-2)(x^2 + 2x + 4)(\sqrt{x+2} + 2)}{x-2} = (x^2 + 2x + 4)(\sqrt{x+2} + 2) for x2x \neq 2.
Now, we can take the limit as x2x \to 2:
limx2(x2+2x+4)(x+2+2)=(22+2(2)+4)(2+2+2)=(4+4+4)(4+2)=(12)(2+2)=(12)(4)=48lim_{x \to 2} (x^2 + 2x + 4)(\sqrt{x+2} + 2) = (2^2 + 2(2) + 4)(\sqrt{2+2} + 2) = (4 + 4 + 4)(\sqrt{4} + 2) = (12)(2+2) = (12)(4) = 48.

3. Final Answer

48

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