Problem

Analyse II
Exercice I
Déterminer les primitives suivantes :
1) $\int \frac{1}{5+x^{2}} d x$
3) $\int \frac{\ln x}{x} d x$.
2) $\int \frac{1}{\sqrt{x^{2}-5}} d x$.
4) $\int \cos ^{3}(x) d x$
Exercice II
Calculer les intégrales :
1) $\int_{0}^{1} \frac{\arctan (x)}{1+x^{2}} d x$.
3) $\int_{0}^{1} \frac{3 x+1}{(x+1)^{2}} d x$.
2) $\int_{1}^{2} x^{2} \ln (x) d x$
4) $\int_{0}^{1} \frac{1}{\left(1+x^{2}\right)^{2}} d x$
Exercice III
1) Déterminer les réels $a, b, c$ tels que pour tout $u$ différent de $\frac{1}{2}$ :
\[
\frac{u^{2}-1}{2 u-1}=a u+b+\frac{c}{2 u-1}
\]
2) Calculer $\int_{-1}^{0} \frac{x^{2}-1}{2 x-1} d x$
3) Calculer $\int_{\frac{-\pi}{6}}^{0} \frac{\cos ^{3} x}{1-2 \sin x} d x$.
Exercice IV
Calculer les intégrales suivantes :
1) $\int_{2}^{3} \frac{1}{x(x-1)} d x$
2) $\int_{2}^{3} \frac{2 x+1}{x^{2}-1} d x$
3) $\int_{0}^{\frac{1}{2}} \frac{x+1}{\left(x^{2}+1\right)(x-2)} d x$.

Answer

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Answer

\(\boxed{\int \frac{1}{5+x^{2}} d x = \frac{1}{\sqrt{5}} \arctan(\frac{x}{\sqrt{5}}) + C}\)

Steps

Step 1 :\(\int \frac{1}{5+x^{2}} d x = \int \frac{1}{5(1+(\frac{x}{\sqrt{5}})^{2})} d x\)

Step 2 :Substitute \(u = \frac{x}{\sqrt{5}}\), then \(du = \frac{1}{\sqrt{5}} dx\)

Step 3 :\(\int \frac{1}{5+x^{2}} d x = \int \frac{1}{5(1+u^{2})} \sqrt{5} du\)

Step 4 :\(\int \frac{1}{5+x^{2}} d x = \frac{1}{\sqrt{5}} \int \frac{1}{1+u^{2}} du\)

Step 5 :\(\int \frac{1}{5+x^{2}} d x = \frac{1}{\sqrt{5}} \arctan(u) + C\)

Step 6 :Substitute back \(u = \frac{x}{\sqrt{5}}\)

Step 7 :\(\int \frac{1}{5+x^{2}} d x = \frac{1}{\sqrt{5}} \arctan(\frac{x}{\sqrt{5}}) + C\)

Step 8 :\(\boxed{\int \frac{1}{5+x^{2}} d x = \frac{1}{\sqrt{5}} \arctan(\frac{x}{\sqrt{5}}) + C}\)

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