Math Problem Statement

\lim_(x->0^(+))x^(sinx)

Solution

To evaluate the limit

limx0+xsinx,\lim_{x \to 0^+} x^{\sin x},

we'll proceed as follows:


Step 1: Rewrite the expression

The term xsinxx^{\sin x} can be rewritten using the exponential function: xsinx=esinxlnx.x^{\sin x} = e^{\sin x \cdot \ln x}.

So, the limit becomes: limx0+xsinx=limx0+esinxlnx.\lim_{x \to 0^+} x^{\sin x} = \lim_{x \to 0^+} e^{\sin x \cdot \ln x}.

Since the exponential function eye^y is continuous, this reduces to: elimx0+(sinxlnx).e^{\lim_{x \to 0^+} (\sin x \cdot \ln x)}.


Step 2: Analyze sinxlnx\sin x \cdot \ln x

As x0+x \to 0^+:

  • sinx0\sin x \to 0, and
  • lnx\ln x \to -\infty.

Thus, the product sinxlnx\sin x \cdot \ln x has an indeterminate form 0()0 \cdot (-\infty). To resolve this, rewrite it: sinxlnx=lnxsinx=lnx1/sinx.\sin x \cdot \ln x = \ln x \cdot \sin x = \frac{\ln x}{1/\sin x}.

Now, as x0+x \to 0^+, sinx0\sin x \to 0, so 1/sinx1/\sin x \to \infty. This results in the new indeterminate form \frac{-\infty}{\infty}, which allows us to apply L'Hôpital's Rule.


Step 3: Apply L’Hôpital’s Rule

We evaluate: limx0+lnx1/sinx.\lim_{x \to 0^+} \frac{\ln x}{1/\sin x}.

Differentiating the numerator and denominator:

  • The derivative of lnx\ln x is 1x\frac{1}{x},
  • The derivative of 1/sinx1/\sin x is cosxsin2x-\frac{\cos x}{\sin^2 x}.

Thus: limx0+lnx1/sinx=limx0+1xcosxsin2x=limx0+sin2xxcosx.\lim_{x \to 0^+} \frac{\ln x}{1/\sin x} = \lim_{x \to 0^+} \frac{\frac{1}{x}}{-\frac{\cos x}{\sin^2 x}} = \lim_{x \to 0^+} \frac{-\sin^2 x}{x \cos x}.


Step 4: Simplify the new expression

As x0+x \to 0^+:

  • sin2x0\sin^2 x \to 0,
  • x0x \to 0,
  • cosx1\cos x \to 1.

The expression simplifies to: sin2xxcosx=sin2xx.\frac{-\sin^2 x}{x \cos x} = \frac{-\sin^2 x}{x}.

We now focus on sin2xx\frac{\sin^2 x}{x}. Using the small-angle approximation sinxx\sin x \sim x as x0x \to 0: sin2xxx2x=x.\frac{\sin^2 x}{x} \sim \frac{x^2}{x} = x.

Thus: sin2xx0as x0+.\frac{-\sin^2 x}{x} \to 0 \quad \text{as } x \to 0^+.


Step 5: Substitute back

We found that: limx0+sinxlnx=0.\lim_{x \to 0^+} \sin x \cdot \ln x = 0.

Returning to the original limit: limx0+xsinx=e0=1.\lim_{x \to 0^+} x^{\sin x} = e^0 = 1.


Final Answer:

1\boxed{1}


Would you like more details or have any questions? Here are some related concepts for exploration:

  1. Why does xsinxx^{\sin x} need to be rewritten as esinxlnxe^{\sin x \ln x}?
  2. How does the small-angle approximation sinxx\sin x \sim x work for limits?
  3. What are common indeterminate forms resolved by L'Hôpital's Rule?
  4. Why is the exponential function eye^y continuous and critical in limit transformations?
  5. Can you extend this problem to other forms like limx0+xcosx\lim_{x \to 0^+} x^{\cos x}?

Tip: Always rewrite power functions like xfx^f in terms of exponentials for easier limit evaluation!

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Math Problem Analysis

Mathematical Concepts

Limits
Exponential Functions
Logarithmic Properties
Indeterminate Forms
L'Hôpital's Rule

Formulas

x^f = e^{f \cdot \ln x}
Small-angle approximation: \sin x \sim x
L'Hôpital's Rule for indeterminate forms: \lim_{x \to c} \frac{f(x)}{g(x)} = \lim_{x \to c} \frac{f'(x)}{g'(x)}

Theorems

Continuity of the Exponential Function
L'Hôpital's Rule

Suitable Grade Level

Grades 11-12 or Early Undergraduate