We need to evaluate the definite integral: $I = \int (\frac{1}{x} + \frac{4}{x^2} - \frac{5}{\sin^2 x}) dx$

AnalysisDefinite IntegralsIntegrationTrigonometric Functions
2025/6/7

1. Problem Description

We need to evaluate the definite integral:
I=(1x+4x25sin2x)dxI = \int (\frac{1}{x} + \frac{4}{x^2} - \frac{5}{\sin^2 x}) dx

2. Solution Steps

First, we can split the integral into three separate integrals:
I=1xdx+4x2dx5sin2xdxI = \int \frac{1}{x} dx + \int \frac{4}{x^2} dx - \int \frac{5}{\sin^2 x} dx
We can rewrite the second term as:
I=1xdx+4x2dx51sin2xdxI = \int \frac{1}{x} dx + 4 \int x^{-2} dx - 5 \int \frac{1}{\sin^2 x} dx
We know that:
1xdx=lnx+C1\int \frac{1}{x} dx = \ln|x| + C_1
xndx=xn+1n+1+C\int x^n dx = \frac{x^{n+1}}{n+1} + C for n1n \neq -1.
So, x2dx=x2+12+1+C2=x11+C2=1x+C2\int x^{-2} dx = \frac{x^{-2+1}}{-2+1} + C_2 = \frac{x^{-1}}{-1} + C_2 = -\frac{1}{x} + C_2
Also, we know that 1sin2xdx=csc2xdx=cotx+C3\int \frac{1}{\sin^2 x} dx = \int \csc^2 x dx = -\cot x + C_3
Substituting these back into our integral:
I=lnx+4(1x)5(cotx)+CI = \ln|x| + 4(-\frac{1}{x}) - 5(-\cot x) + C
I=lnx4x+5cotx+CI = \ln|x| - \frac{4}{x} + 5\cot x + C

3. Final Answer

I=lnx4x+5cotx+CI = \ln|x| - \frac{4}{x} + 5\cot x + C

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