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Section 3.1 Primitives et propriétés de base

Déterminez la famille de toutes les primitives de la fonction donnée.

  1. \(\displaystyle \displaystyle x^{7/3}\)
  2. \(\displaystyle \displaystyle\cos(9x)\)
  3. \(\displaystyle \displaystyle\sin\left(\frac{x}{5}\right)\)
  4. \(\displaystyle \displaystyle\frac{1}{\sqrt[7]{x^3}}\)
  5. \(\displaystyle \displaystyle\frac{1}{e^{4x}}\)
  6. \(\displaystyle \displaystyle\sec^2(3x)\)
  7. \(\displaystyle \displaystyle\frac{1}{\sin^2\left(\frac{x}{7}\right)}\)
  8. \(\displaystyle \displaystyle\frac{\sin(8x)}{\cos^2(8x)}\)
Réponse
  1. \(\displaystyle \displaystyle \frac{3x^{10/3}}{10}+C\)
  2. \(\displaystyle \displaystyle\frac{\sin(9x)}{9}+C\)
  3. \(\displaystyle \displaystyle-5\cos\left(\frac{x}{5}\right)+C\)
  4. \(\displaystyle \displaystyle7\frac{\sqrt[7]{x^4}}{4}+C\)
  5. \(\displaystyle \displaystyle-\frac{1}{4e^{4x}}+C\)
  6. \(\displaystyle \displaystyle\frac{\tan(3x)}{3}+C\)
  7. \(\displaystyle \displaystyle-7\cot\left(\frac{x}{7}\right)+C\)
  8. \(\displaystyle \displaystyle\frac{\sec(8x)}{8}+C\)

Vérifiez que la fonction \(F(x)\) est une primitive de la fonction \(f(x)\text{,}\) puis évaluez l'intégrale demandée en utilisant le théorème fondamental du calcul intégral.

  1. \(\displaystyle F(x)=x\ln(x)-x\text{,}\) \(\displaystyle f(x)=\ln(x)\text{,}\) \(\displaystyle I=\int_e^{e^2}\ln(x)dx\)
  2. \(\displaystyle F(x)=\frac{x}{2}+\frac{\sin(2x)}{4}\text{,}\) \(\displaystyle f(x)=\cos^2(x)\text{,}\) \(\displaystyle I=\int_0^{\frac{\pi}{3}}\cos^2(x)dx\)
  3. \(\displaystyle F(x)=\frac{1}{3}\arctan\left(\frac{x}{3}\right)\text{,}\) \(\displaystyle f(x)=\frac{1}{x^2+9}\text{,}\) \(\displaystyle I=\int_0^{\frac{3\pi}{4}}\frac{1}{x^2+9}dx\)
  4. \(\displaystyle F(x)=\frac{9}{2}\arcsin\left(\frac{x}{3}\right)+\frac{x\sqrt{9-x^2}}{2}\text{,}\) \(\displaystyle f(x)=\sqrt{9-x^2}\text{,}\) \(\displaystyle I=\int_0^3\sqrt{9-x^2}dx\)
  5. \(\displaystyle F(x)=\ln\left(x+\sqrt{x^2-9}\right)\text{,}\) \(\displaystyle f(x)=\frac{1}{\sqrt{x^2-9}}\text{,}\) \(\displaystyle I=\int_3^5\frac{1}{\sqrt{x^2-9}}dx\)
Réponse
  1. \(\displaystyle \displaystyle I=e^2\)
  2. \(\displaystyle \displaystyle I=\frac{\pi}{6}+\frac{\sqrt{3}}{8}\)
  3. \(\displaystyle \displaystyle I=\frac{1}{3}\)
  4. \(\displaystyle \displaystyle I=\frac{9\pi}{4}\)
  5. \(\displaystyle \displaystyle I=\ln(3)\)

Sachant que \(\displaystyle\int_1^5f(x)\;dx=7\text{,}\) \(\displaystyle\int_0^1f(x)\;dx=-4\text{,}\) \(\displaystyle\int_5^7f(x)\;dx=0\) et \(\displaystyle\int_5^7g(x)\;dx=-2\text{,}\) utilisez les propriétés de l'intégrale définie pour évaluer les intégrales suivantes.

  1. \(\displaystyle\int_5^1f(x)\;dx\)

  2. \(\displaystyle\int_0^5f(x)\;dx\)

  3. \(\displaystyle\int_7^0f(x)\;dx\)

  4. \(\displaystyle\int_7^54g(x)\;dx\)

  5. \(\displaystyle\int_5^7(3f(x)-9g(x))\;dx\)

Réponse
  1. \(\displaystyle -7\)

  2. \(\displaystyle 3\)

  3. \(\displaystyle -3\)

  4. \(\displaystyle 8\)

  5. \(\displaystyle 18\)