Math Problem Statement

Evaluate the limit: lim (x → 0) (sqrt(3x + 49) - 7) / x

Solution

The limit presented in the image is:

limx03x+497x\lim_{{x \to 0}} \frac{\sqrt{3x + 49} - 7}{x}

To solve this limit, we can use algebraic techniques like multiplying by the conjugate of the numerator to eliminate the square root. Here are the steps:

Step 1: Multiply by the conjugate

Multiply both the numerator and denominator by the conjugate of the numerator, which is 3x+49+7\sqrt{3x + 49} + 7:

3x+497x3x+49+73x+49+7=(3x+497)(3x+49+7)x(3x+49+7)\frac{\sqrt{3x + 49} - 7}{x} \cdot \frac{\sqrt{3x + 49} + 7}{\sqrt{3x + 49} + 7} = \frac{\left(\sqrt{3x + 49} - 7\right)\left(\sqrt{3x + 49} + 7\right)}{x\left(\sqrt{3x + 49} + 7\right)}

Step 2: Simplify the numerator

The numerator becomes a difference of squares:

(3x+49)272=(3x+49)49=3x(\sqrt{3x + 49})^2 - 7^2 = (3x + 49) - 49 = 3x

Thus, the expression simplifies to:

3xx(3x+49+7)\frac{3x}{x(\sqrt{3x + 49} + 7)}

Step 3: Cancel xx

We can cancel xx from the numerator and denominator:

33x+49+7\frac{3}{\sqrt{3x + 49} + 7}

Step 4: Evaluate the limit

Now, take the limit as x0x \to 0:

limx033x+49+7=33(0)+49+7=349+7=37+7=314\lim_{{x \to 0}} \frac{3}{\sqrt{3x + 49} + 7} = \frac{3}{\sqrt{3(0) + 49} + 7} = \frac{3}{\sqrt{49} + 7} = \frac{3}{7 + 7} = \frac{3}{14}

Final Answer:

The value of the limit is 314\frac{3}{14}.

Would you like more details on any step?

Here are some related questions for further exploration:

  1. How does multiplying by the conjugate help simplify expressions?
  2. Can limits involving square roots always be solved using conjugates?
  3. What is the general form of a difference of squares?
  4. What other techniques can be used to evaluate limits at indeterminate forms?
  5. How does this limit compare to L'Hopital's rule for solving indeterminate forms?

Tip: Whenever you encounter square roots in limits, using conjugates to eliminate the square root is often an effective strategy!

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Math Problem Analysis

Mathematical Concepts

Limits
Algebraic Manipulation
Square Roots

Formulas

Difference of squares: (a - b)(a + b) = a^2 - b^2
Limit definition and evaluation

Theorems

Conjugate technique for simplifying square roots
Difference of squares

Suitable Grade Level

Grades 11-12