Math Problem Statement

Can’t you find it other way than h’lopital

Solution

Certainly! We can solve this limit problem without using L'Hôpital's Rule by leveraging the Taylor series expansion for sin(x)\sin(x) or by simplifying the expression using algebraic techniques.

Step 1: Use the Taylor Series Expansion

The Taylor series expansion of sin(x)\sin(x) around x=0x = 0 is:

sin(x)=xx36+higher-order terms\sin(x) = x - \frac{x^3}{6} + \text{higher-order terms}

For small values of xx, we can approximate sin(x)\sin(x) by its first term:

sin(x)x\sin(x) \approx x

Step 2: Simplify the Expression

Substitute this approximation into the limit:

limx05x2+9xsin(x)limx05x2+9xx\lim_{{x \to 0}} \frac{5x^2 + 9x}{\sin(x)} \approx \lim_{{x \to 0}} \frac{5x^2 + 9x}{x}

Now, factor the numerator:

limx0x(5x+9)x\lim_{{x \to 0}} \frac{x(5x + 9)}{x}

Step 3: Simplify Further

Cancel the xx terms in the numerator and denominator (note that x0x \neq 0 for this cancellation):

limx0(5x+9)\lim_{{x \to 0}} (5x + 9)

Step 4: Evaluate the Limit

Now, directly substitute x=0x = 0 into the simplified expression:

5(0)+9=95(0) + 9 = 9

Thus, the limit is:

limx05x2+9xsin(x)=9\lim_{{x \to 0}} \frac{5x^2 + 9x}{\sin(x)} = 9

This method avoids the use of L'Hôpital's Rule by using the approximation for sin(x)\sin(x) and straightforward algebra.

Do you have any more questions or would you like to explore other approaches?

Here are five related questions for further exploration:

  1. How does the Taylor series for sin(x)\sin(x) help in finding limits?
  2. Can you generalize the process for finding limits involving small-angle approximations?
  3. What would the limit be if the numerator were x3x^3 instead of 5x2+9x5x^2 + 9x?
  4. How can we justify the cancellation of xx in the numerator and denominator?
  5. How does this approach differ from using L'Hôpital's Rule in terms of understanding the behavior of the function?

Tip: Small-angle approximations like sin(x)x\sin(x) \approx x are extremely useful for solving limits, especially when xx approaches zero.

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Math Problem Analysis

Mathematical Concepts

Limits
Taylor Series Expansion
Algebraic Techniques

Formulas

Taylor series expansion for sin(x)

Theorems

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Suitable Grade Level

Advanced High School