Chapter 10: Problem 3
\(\lim _{x \rightarrow 0} \frac{\sin 9 x}{\sin 7 x}\)
Short Answer
Expert verified
The limit is \(\frac{9}{7}\).
Step by step solution
01
Recall the Sine Limit Property
Recall that \(\frac{\text{sin}(x)}{x} \rightarrow 1 \text{ as } x \rightarrow 0\). This will help simplify the expression.
02
Rewrite the Expression
Rewrite the given limit in terms of the property: \(\frac{\text{sin}(9x)}{\text{sin}(7x)} = \frac{\text{sin}(9x)/(9x)}{\text{sin}(7x)/(7x)} \times \frac{9x}{7x}\).
03
Apply the Limit
Apply the limit using the property from Step 1. Recognize that, as \( x \rightarrow 0 \), \( \frac{\text{sin}(9x)}{9x} \rightarrow 1\) and \( \frac{\text{sin}(7x)}{7x} \rightarrow 1\). This leaves us with: \(\frac{1}{1} \times \frac{9x}{7x} = \frac{9}{7} \).
04
Confirm the Result
After applying the limits, confirm the result: \( \frac{9}{7} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Sine Function
The sine function, often written as \(\text{sin}(x)\), is a fundamental function in trigonometry. It's essential to understand how it behaves, especially as the input approaches certain values.
- The sine function is periodic with a period of 2\( \pi \).
- When the input value, x, approaches 0, \(\text{sin}(x)\) behaves very predictably.
- This predictable behavior is crucial in calculus as it forms the basis for various limit properties.
Limit Properties
Limits are a core concept in calculus. A limit evaluates what a function's output approaches as the input approaches a particular value.
- One vital property is the limit of the sine function as the input approaches zero.
- If you encounter \(\frac{\text{sin}(x)}{x}\), it approaches 1 as x approaches 0. This is because \(\text{sin}(x)\) starts to behave like x for very small values.
Trigonometric Limits
Trigonometric limits specifically deal with limits involving trigonometric functions like sine, cosine, and tangent.
- These limits are crucial because trigonometric functions often arise in various calculus problems.
- A key limit to remember is \( \lim_{x \to 0} \frac{\text{sin}(x)}{x} = 1 \). This serves as a foundation for solving more complex trigonometric limits.
L'Hôpital's Rule
L'Hôpital's Rule is a powerful tool for evaluating limits, especially when direct substitution in limit problems results in indeterminate forms, like \( \frac{0}{0} \) or \( \frac{\text{infinity}}{\text{infinity}} \).
- The rule states that if \(\frac{f(x)}{g(x)}\) approaches \( \frac{0}{0} \) or \( \frac{\text{infinity}}{\text{infinity}} \), then \( \lim_{x \to c} \frac{f(x)}{g(x)} = \lim_{x \to c} \frac{f'(x)}{g'(x)} \).
- This means you can differentiate the numerator and the denominator separately and then take the limit of the resulting function.