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Math

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PROBLEM

Evaluate limx7x+23x249\lim _{x \rightarrow 7} \frac{\sqrt{x+2}-3}{x^{2}-49}

STEP 1

1. We are given the limit expression limx7x+23x249\lim _{x \rightarrow 7} \frac{\sqrt{x+2}-3}{x^{2}-49}.
2. We need to evaluate this limit as xx approaches 7.

STEP 2

1. Substitute x=7x = 7 into the expression to check for indeterminate form.
2. Simplify the expression using algebraic techniques.
3. Re-evaluate the limit after simplification.

STEP 3

Substitute x=7x = 7 into the expression:
7+237249=934949=330=00\frac{\sqrt{7+2}-3}{7^{2}-49} = \frac{\sqrt{9}-3}{49-49} = \frac{3-3}{0} = \frac{0}{0} The expression is in the indeterminate form 00\frac{0}{0}.

STEP 4

Simplify the expression by rationalizing the numerator. Multiply the numerator and the denominator by the conjugate of the numerator:
x+23x249x+2+3x+2+3=(x+23)(x+2+3)(x249)(x+2+3)\frac{\sqrt{x+2}-3}{x^{2}-49} \cdot \frac{\sqrt{x+2}+3}{\sqrt{x+2}+3} = \frac{(\sqrt{x+2}-3)(\sqrt{x+2}+3)}{(x^{2}-49)(\sqrt{x+2}+3)}

STEP 5

Simplify the numerator using the difference of squares:
(x+23)(x+2+3)=(x+2)232=x+29=x7(\sqrt{x+2}-3)(\sqrt{x+2}+3) = (\sqrt{x+2})^2 - 3^2 = x+2 - 9 = x - 7

STEP 6

Factor the denominator:
x249=(x7)(x+7)x^{2} - 49 = (x-7)(x+7)

STEP 7

Substitute the simplified numerator and denominator back into the expression:
x7(x7)(x+7)(x+2+3)\frac{x - 7}{(x-7)(x+7)(\sqrt{x+2}+3)} Cancel the common factor (x7)(x-7):
1(x+7)(x+2+3)\frac{1}{(x+7)(\sqrt{x+2}+3)}

SOLUTION

Re-evaluate the limit as xx approaches 7:
limx71(x+7)(x+2+3)=1(7+7)(7+2+3)\lim _{x \rightarrow 7} \frac{1}{(x+7)(\sqrt{x+2}+3)} = \frac{1}{(7+7)(\sqrt{7+2}+3)} Simplify:
=114×(3+3)=114×6=184= \frac{1}{14 \times (3+3)} = \frac{1}{14 \times 6} = \frac{1}{84} The value of the limit is:
184\boxed{\frac{1}{84}}

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