Math Problem Statement

lim x→1  (x − 1) sin  2 √x  1

Solution

To solve the limit:

limx1(x1)sin(2x)\lim_{{x \to 1}} (x - 1) \sin\left(2\sqrt{x}\right)

Let's go step by step:

Step 1: Substituting x=1x = 1 directly

When we substitute x=1x = 1, the expression becomes:

(11)sin(21)=0×sin(2)=0(1 - 1) \sin(2\sqrt{1}) = 0 \times \sin(2) = 0

This gives an indeterminate form 0×sin(2)=00 \times \sin(2) = 0. We need a more careful evaluation, such as using L'Hopital's Rule or another method.

Step 2: Using L'Hopital's Rule

L'Hopital's Rule applies to indeterminate forms like 0×0 \times \infty or 00\frac{0}{0}. We can rewrite the expression to apply it:

limx1(x1)sin(2x)=limx1sin(2x)1x1\lim_{{x \to 1}} (x - 1) \sin(2\sqrt{x}) = \lim_{{x \to 1}} \frac{\sin(2\sqrt{x})}{\frac{1}{x - 1}}

We now have the indeterminate form 00\frac{0}{0}, so we can apply L'Hopital's Rule by differentiating the numerator and denominator:

Derivative of the numerator:

ddx(sin(2x))=cos(2x)ddx(2x)=cos(2x)1x\frac{d}{dx} \left( \sin(2\sqrt{x}) \right) = \cos(2\sqrt{x}) \cdot \frac{d}{dx} (2\sqrt{x}) = \cos(2\sqrt{x}) \cdot \frac{1}{\sqrt{x}}

Derivative of the denominator:

ddx(1x1)=1(x1)2\frac{d}{dx} \left( \frac{1}{x - 1} \right) = -\frac{1}{(x - 1)^2}

Step 3: Applying L'Hopital's Rule

Now, evaluate the limit:

limx1cos(2x)1x1(x1)2\lim_{{x \to 1}} \frac{\cos(2\sqrt{x}) \cdot \frac{1}{\sqrt{x}}}{-\frac{1}{(x - 1)^2}}

This limit should simplify to 0. Therefore, the original limit is:

limx1(x1)sin(2x)=0\lim_{{x \to 1}} (x - 1) \sin(2\sqrt{x}) = 0

Let me know if you'd like more details, or if you have any further questions!


Here are 5 related questions for further practice:

  1. What is the limit limx0xsin(1x)\lim_{{x \to 0}} x \sin\left(\frac{1}{x}\right)?
  2. How does L'Hopital's Rule apply to indeterminate forms?
  3. What is the derivative of sin(3x2)\sin(3x^2)?
  4. Can you find the limit of limx1x21x1\lim_{{x \to 1}} \frac{x^2 - 1}{x - 1}?
  5. What is the Taylor expansion of sin(x)\sin(x) around x=0x = 0?

Tip: Always check if the limit gives an indeterminate form like 00\frac{0}{0} or ×0\infty \times 0 before applying L'Hopital's Rule.

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Math Problem Analysis

Mathematical Concepts

Limits
Trigonometric Functions
L'Hopital's Rule

Formulas

L'Hopital's Rule: lim x→c f(x)/g(x) = lim x→c f'(x)/g'(x), when indeterminate forms like 0/0 appear
Derivative of sin(2√x): d/dx[sin(2√x)] = cos(2√x) * 1/√x

Theorems

L'Hopital's Rule

Suitable Grade Level

Undergraduate Calculus