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Solve the following integration problems: i) integral (x+1)sqrt(2x+x2)\,dx ii) integral01 t t\,dt

Mathematics

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Here are the solutions to the integration problems.

1. i) ∫(x+1)2x+x2 dx\int (x+1)\sqrt{2x+x^2}\,dx

  1. Use substitution.

    Let u=2x+x2u = 2x+x^2.
    Then, differentiate uu with respect to xx:

    dudx=2+2x=2(1+x)\frac{du}{dx} = 2 + 2x = 2(1+x)

    So, du=2(1+x) dxdu = 2(1+x)\,dx, which means (1+x) dx=12 du(1+x)\,dx = \frac{1}{2}\,du.

  2. Substitute uu and dudu into the integral.

    ∫(x+1)2x+x2 dx=∫u⋅12 du\int (x+1)\sqrt{2x+x^2}\,dx = \int \sqrt{u} \cdot \frac{1}{2}\,du =12∫u1/2 du= \frac{1}{2} \int u^{1/2}\,du
  3. Integrate with respect to uu.

    12⋅u1/2+11/2+1+C=12⋅u3/23/2+C\frac{1}{2} \cdot \frac{u^{1/2+1}}{1/2+1} + C = \frac{1}{2} \cdot \frac{u^{3/2}}{3/2} + C =12⋅23u3/2+C=13u3/2+C= \frac{1}{2} \cdot \frac{2}{3} u^{3/2} + C = \frac{1}{3} u^{3/2} + C
  4. Substitute back u=2x+x2u = 2x+x^2.

    13(2x+x2)3/2+C\frac{1}{3} (2x+x^2)^{3/2} + C

    The final answer is 13(2x+x2)3/2+C\boxed{\frac{1}{3} (2x+x^2)^{3/2} + C}.

    1. ii) ∫01tcosh⁡t dt\int_0^1 t \cosh t\,dt

  5. Use integration by parts, ∫u dv=uv−∫v du\int u\,dv = uv - \int v\,du.

    Let u=tu = t and dv=cosh⁡t dtdv = \cosh t\,dt.
    Then, du=dtdu = dt and v=∫cosh⁡t dt=sinh⁡tv = \int \cosh t\,dt = \sinh t.

  6. Apply the integration by parts formula.

    ∫tcosh⁡t dt=tsinh⁡t−∫sinh⁡t dt\int t \cosh t\,dt = t \sinh t - \int \sinh t\,dt =tsinh⁡t−cosh⁡t+C= t \sinh t - \cosh t + C
  7. Evaluate the definite integral from 0 to 1.

    [tsinh⁡t−cosh⁡t]01=(1⋅sinh⁡1−cosh⁡1)−(0⋅sinh⁡0−cosh⁡0)[t \sinh t - \cosh t]_0^1 = (1 \cdot \sinh 1 - \cosh 1) - (0 \cdot \sinh 0 - \cosh 0)

    We know that sinh⁡0=0\sinh 0 = 0 and cosh⁡0=1\cosh 0 = 1.

    =(sinh⁡1−cosh⁡1)−(0−1)= (\sinh 1 - \cosh 1) - (0 - 1) =sinh⁡1−cosh⁡1+1= \sinh 1 - \cosh 1 + 1

    Using the definitions sinh⁡x=ex−e−x2\sinh x = \frac{e^x - e^{-x}}{2} and cosh⁡x=ex+e−x2\cosh x = \frac{e^x + e^{-x}}{2}:

    sinh⁡1−cosh⁡1=e1−e−12−e1+e−12\sinh 1 - \cosh 1 = \frac{e^1 - e^{-1}}{2} - \frac{e^1 + e^{-1}}{2} =e−e−1−e−e−12=−2e−12=−e−1= \frac{e - e^{-1} - e - e^{-1}}{2} = \frac{-2e^{-1}}{2} = -e^{-1}

    So, the expression becomes:

    −e−1+1-e^{-1} + 1

    The final answer is 1−e−1\boxed{1 - e^{-1}}.

    2. i) ∫sec⁡2(1/x)x2 dx\int \frac{\sec^2(1/x)}{x^2}\,dx

  8. Use substitution.

    Let u=1x=x−1u = \frac{1}{x} = x^{-1}.
    Then, differentiate uu with respect to xx:

    dudx=−1⋅x−2=−1x2\frac{du}{dx} = -1 \cdot x^{-2} = -\frac{1}{x^2}

    So, du=−1x2 dxdu = -\frac{1}{x^2}\,dx, which means 1x2 dx=−du\frac{1}{x^2}\,dx = -du.

  9. Substitute uu and dudu into the integral.

    ∫sec⁡2(1/x)x2 dx=∫sec⁡2(u)(−du)\int \frac{\sec^2(1/x)}{x^2}\,dx = \int \sec^2(u) (-du) =−∫sec⁡2(u) du= -\int \sec^2(u)\,du
  10. Integrate with respect to uu.

    −tan⁡u+C-\tan u + C
  11. Substitute back u=1/xu = 1/x.

    −tan⁡(1/x)+C-\tan(1/x) + C

    The final answer is −tan⁡(1/x)+C\boxed{-\tan(1/x) + C}.

    2. ii) ∫sin⁡(ln⁡x)x dx\int \frac{\sin(\ln x)}{x}\,dx

  12. Use substitution.

    Let u=ln⁡xu = \ln x.
    Then, differentiate uu with respect to xx:

    dudx=1x\frac{du}{dx} = \frac{1}{x}

    So, du=1x dxdu = \frac{1}{x}\,dx.

  13. Substitute uu and dudu into the integral.

    ∫sin⁡(ln⁡x)x dx=∫sin⁡(u) du\int \frac{\sin(\ln x)}{x}\,dx = \int \sin(u)\,du
  14. Integrate with respect to uu.

    −cos⁡u+C-\cos u + C
  15. Substitute back u=ln⁡xu = \ln x.

    −cos⁡(ln⁡x)+C-\cos(\ln x) + C

    The final answer is −cos⁡(ln⁡x)+C\boxed{-\cos(\ln x) + C}.

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