Math Problem Statement

lim(x→π/3) [(sin(x) - √3 cos(x)) / sin(3x)]

Solution

The limit expression extracted from the image seems to be:

limxπ3sinx3cosxsin3x\lim_{x \to \frac{\pi}{3}} \frac{\sin{x} - \sqrt{3} \cos{x}}{\sin{3x}}

Let me now proceed to solve this limit step by step.


We begin by substituting x=π3x = \frac{\pi}{3} into the numerator and denominator.

Step 1: Substitution

Numerator: sin(π3)3cos(π3)\sin\left(\frac{\pi}{3}\right) - \sqrt{3} \cos\left(\frac{\pi}{3}\right) Denominator: sin(3×π3)=sin(π)\sin\left( 3 \times \frac{\pi}{3} \right) = \sin(\pi)

Since sin(π)=0\sin(\pi) = 0, we have an indeterminate form 00\frac{0}{0}, meaning L'Hôpital's rule applies.

Step 2: L'Hôpital's Rule

We differentiate the numerator and denominator:

Numerator: ddx(sinx3cosx)=cosx+3sinx\frac{d}{dx} \left( \sin{x} - \sqrt{3} \cos{x} \right) = \cos{x} + \sqrt{3} \sin{x}

Denominator: ddx(sin3x)=3cos3x\frac{d}{dx} \left( \sin{3x} \right) = 3 \cos{3x}

Step 3: Evaluate the new limit

Now, the limit becomes: limxπ3cosx+3sinx3cos3x\lim_{x \to \frac{\pi}{3}} \frac{\cos{x} + \sqrt{3} \sin{x}}{3 \cos{3x}}

Substitute x=π3x = \frac{\pi}{3} again:

  • cos(π3)=12\cos\left( \frac{\pi}{3} \right) = \frac{1}{2}
  • sin(π3)=32\sin\left( \frac{\pi}{3} \right) = \frac{\sqrt{3}}{2}
  • cos(3×π3)=cos(π)=1\cos(3 \times \frac{\pi}{3}) = \cos(\pi) = -1

Thus, the limit becomes: 12+3×323×(1)=12+323=23=23\frac{\frac{1}{2} + \sqrt{3} \times \frac{\sqrt{3}}{2}}{3 \times (-1)} = \frac{\frac{1}{2} + \frac{3}{2}}{-3} = \frac{2}{-3} = -\frac{2}{3}

Final Answer:

limxπ3sinx3cosxsin3x=23\lim_{x \to \frac{\pi}{3}} \frac{\sin{x} - \sqrt{3} \cos{x}}{\sin{3x}} = -\frac{2}{3}


Would you like further details on the steps or explanations? Here are five related questions you can explore:

  1. How does L'Hôpital's rule apply to other indeterminate forms like \frac{\infty}{\infty}?
  2. What are the common indeterminate forms that appear in limit problems?
  3. Can we apply a Taylor series expansion to solve limits at points other than 0?
  4. What are other techniques for evaluating trigonometric limits without using L'Hôpital's rule?
  5. How do derivatives of trigonometric functions help in solving limit problems?

Tip: Always check for indeterminate forms before applying L'Hôpital's rule to ensure it's valid.

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Math Problem Analysis

Mathematical Concepts

Limits
Trigonometry
L'Hôpital's Rule

Formulas

sin(π/3) = √3/2
cos(π/3) = 1/2
L'Hôpital's Rule: lim(f(x)/g(x)) = lim(f'(x)/g'(x)) for indeterminate forms

Theorems

L'Hôpital's Rule

Suitable Grade Level

Grades 11-12 or early university