Math Problem Statement

Evaluate the integral from π/4 to π/3 of dx / sin(2x)

Solution

The integral presented in the image is:

π4π3dxsin(2x)\int_{\frac{\pi}{4}}^{\frac{\pi}{3}} \frac{dx}{\sin(2x)}

To solve this, we will follow these steps:

Step 1: Use the identity for sin(2x)\sin(2x)

Recall that:

sin(2x)=2sin(x)cos(x)\sin(2x) = 2 \sin(x) \cos(x)

So, the integral becomes:

π4π3dx2sin(x)cos(x)\int_{\frac{\pi}{4}}^{\frac{\pi}{3}} \frac{dx}{2 \sin(x) \cos(x)}

Step 2: Simplify the integral

We can express 1sin(2x)\frac{1}{\sin(2x)} as:

1sin(2x)=12sin(x)cos(x)=12(1sin(x)cos(x))\frac{1}{\sin(2x)} = \frac{1}{2 \sin(x) \cos(x)} = \frac{1}{2} \left( \frac{1}{\sin(x) \cos(x)} \right)

Now, observe that:

1sin(x)cos(x)=2sin(2x)\frac{1}{\sin(x) \cos(x)} = \frac{2}{\sin(2x)}

Thus, the integral becomes:

12π4π3dxsin(2x)\frac{1}{2} \int_{\frac{\pi}{4}}^{\frac{\pi}{3}} \frac{dx}{\sin(2x)}

Step 3: Evaluate the integral

The integral of 1sin(2x)\frac{1}{\sin(2x)} is the logarithmic function of tan(x)\tan(x), giving us:

dxsin(2x)=12lncot(x)\int \frac{dx}{\sin(2x)} = -\frac{1}{2} \ln \left| \cot(x) \right|

Evaluating this from π4\frac{\pi}{4} to π3\frac{\pi}{3}:

12(lncot(π3)lncot(π4))-\frac{1}{2} \left( \ln \left| \cot \left( \frac{\pi}{3} \right) \right| - \ln \left| \cot \left( \frac{\pi}{4} \right) \right| \right)

Now, calculating these values:

  • cot(π3)=13\cot \left( \frac{\pi}{3} \right) = \frac{1}{\sqrt{3}}
  • cot(π4)=1\cot \left( \frac{\pi}{4} \right) = 1

So, we have:

12(ln(13)ln(1))=12(12ln(3))-\frac{1}{2} \left( \ln \left( \frac{1}{\sqrt{3}} \right) - \ln(1) \right) = -\frac{1}{2} \left( -\frac{1}{2} \ln(3) \right)

Thus, the final value is:

14ln(3)\frac{1}{4} \ln(3)

Therefore, the value of the definite integral is:

14ln(3)\boxed{\frac{1}{4} \ln(3)}

Would you like further details or clarifications on any steps?


Here are 5 related questions to explore:

  1. How do you compute integrals involving trigonometric identities?
  2. Can integrals of other trigonometric functions be solved similarly?
  3. How does the substitution method work in integral calculus?
  4. What is the geometric interpretation of an integral?
  5. How do definite integrals differ from indefinite integrals?

Tip: When dealing with trigonometric integrals, it's helpful to use known identities to simplify the expressions first before integrating.

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Math Problem Analysis

Mathematical Concepts

Integral Calculus
Trigonometric Integrals

Formulas

sin(2x) = 2 sin(x) cos(x)
Integral of 1/sin(2x)

Theorems

Trigonometric Identity
Definite Integral Evaluation

Suitable Grade Level

Grades 11-12, Undergraduate Calculus