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aaronhou's Question
Math
Posted 9 months ago
this is great
01x31+x2dx=\int_{0}^{1} \frac{x^{3}}{1+x^{2}} d x=
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Answer from Sia
Posted 9 months ago
Solution by Steps
step 1
To integrate the function 01x31+x2dx\int_{0}^{1} \frac{x^{3}}{1+x^{2}} dx, we look for a method to simplify the integrand
step 2
We notice that the derivative of 1+x21+x^2 is 2x2x, which is close to the numerator x3x^3. This suggests a substitution
step 3
Let u=1+x2u = 1+x^2. Then, du=2xdxdu = 2x dx
step 4
We need to adjust the numerator to match our substitution. We can write x3dxx^3 dx as 12x22xdx\frac{1}{2}x^2 \cdot 2x dx
step 5
Substituting uu and dudu into the integral, we get 12u1udu\frac{1}{2}\int \frac{u-1}{u} du
step 6
Split the integral: 1211udu\frac{1}{2}\int 1 - \frac{1}{u} du
step 7
Integrate term by term: 12(ulnu)+C\frac{1}{2}(u - \ln|u|) + C
step 8
Substitute back for uu: 12(x2lnx2+1)+C\frac{1}{2}(x^2 - \ln|x^2+1|) + C
step 9
Evaluate the definite integral from 0 to 1: 12[(12ln12+1)(02ln02+1)]\frac{1}{2}[(1^2 - \ln|1^2+1|) - (0^2 - \ln|0^2+1|)]
step 10
Simplify to get the final answer: 12(1ln(2))\frac{1}{2}(1 - \ln(2))
Answer
12(1ln(2))0.15343\frac{1}{2}(1 - \ln(2)) \approx 0.15343
Key Concept
Integration by Substitution
Explanation
To integrate a function of the form xn1+x2\frac{x^n}{1+x^2}, where nn is an odd integer, we can use substitution with u=1+x2u = 1+x^2, simplifying the integration process.

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