Math Problem Statement

Find the limit. (If an answer does not exist, enter DNE.) lim x→0 sin 2x sin 6x

Solution

To solve the limit

limx0sin(2x)sin(6x)\lim_{{x \to 0}} \frac{\sin(2x)}{\sin(6x)}

we can make use of the standard limit result:

limx0sin(kx)kx=1\lim_{{x \to 0}} \frac{\sin(kx)}{kx} = 1

for any constant kk.

Step 1: Rewrite the expression

We can rewrite the limit expression by factoring out the constants 22 and 66 in the sine functions:

limx0sin(2x)sin(6x)=limx0sin(2x)2xsin(6x)6x×26\lim_{{x \to 0}} \frac{\sin(2x)}{\sin(6x)} = \lim_{{x \to 0}} \frac{\frac{\sin(2x)}{2x}}{\frac{\sin(6x)}{6x}} \times \frac{2}{6}

Step 2: Apply the limit property

From the standard limit property, we know:

limx0sin(2x)2x=1andlimx0sin(6x)6x=1\lim_{{x \to 0}} \frac{\sin(2x)}{2x} = 1 \quad \text{and} \quad \lim_{{x \to 0}} \frac{\sin(6x)}{6x} = 1

Thus, we can simplify the limit expression:

limx0sin(2x)sin(6x)=11×26=26=13\lim_{{x \to 0}} \frac{\sin(2x)}{\sin(6x)} = \frac{1}{1} \times \frac{2}{6} = \frac{2}{6} = \frac{1}{3}

Final Answer:

The limit is

13\boxed{\frac{1}{3}}

Would you like more details or have further questions? Here are some related questions to explore:

  1. How does the standard limit limx0sin(kx)kx=1\lim_{{x \to 0}} \frac{\sin(kx)}{kx} = 1 apply to other trigonometric functions like cosine?
  2. What would happen if we had limx0sin(2x)x\lim_{{x \to 0}} \frac{\sin(2x)}{x} instead?
  3. How can we use L'Hôpital's Rule to evaluate limits of indeterminate forms like 00\frac{0}{0}?
  4. What are some other common limits used in calculus for evaluating trigonometric expressions?
  5. Can this approach be extended to limits involving more complicated trigonometric functions, such as tan(x)\tan(x)?

Tip: When dealing with limits involving trigonometric functions as x0x \to 0, remember the key result limx0sin(x)x=1\lim_{{x \to 0}} \frac{\sin(x)}{x} = 1, which is crucial in simplifying many such expressions.

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Math Problem Analysis

Mathematical Concepts

Limits
Trigonometric Functions
Simplification of Expressions

Formulas

lim(x→0) [sin(kx)/kx] = 1 for any constant k
lim(x→0) [sin(a)/sin(b)] = (a/b) for small angles a and b

Theorems

Standard limit theorem for sin(x)/x
Properties of limits

Suitable Grade Level

Grades 11-12 or Calculus I