Math Problem Statement

Evaluate the triple integral \(\int_0^{\frac{\pi}{2}} \int_0^z \int_0^y \sin(x + y + z) \, dx \, dy \, dz\).

Solution

The given image shows a triple integral of the following form:

0π20z0ysin(x+y+z)dxdydz\int_0^{\frac{\pi}{2}} \int_0^z \int_0^y \sin(x + y + z) \, dx \, dy \, dz

We need to evaluate this integral step-by-step.

Step-by-step solution:

  1. Inner integral (with respect to xx): The first integral is with respect to xx, keeping yy and zz as constants. 0ysin(x+y+z)dx\int_0^y \sin(x + y + z) \, dx To integrate this, let’s use the substitution u=x+y+zu = x + y + z, so du=dxdu = dx. When x=0x = 0, u=y+zu = y + z, and when x=yx = y, u=2y+zu = 2y + z. The integral becomes: y+z2y+zsin(u)du\int_{y+z}^{2y+z} \sin(u) \, du The integral of sin(u)\sin(u) is cos(u)-\cos(u), so this becomes: cos(u)y+z2y+z=cos(2y+z)+cos(y+z)-\cos(u) \Big|_{y+z}^{2y+z} = -\cos(2y+z) + \cos(y+z) Thus, the result of the inner integral is: cos(y+z)cos(2y+z)\cos(y+z) - \cos(2y+z)

  2. Second integral (with respect to yy): Now we need to integrate this result with respect to yy: 0z[cos(y+z)cos(2y+z)]dy\int_0^z [\cos(y+z) - \cos(2y+z)] \, dy For each term:

    • 0zcos(y+z)dy\int_0^z \cos(y+z) \, dy can be simplified using the substitution u=y+zu = y + z. This leads to sin(y+z)\sin(y + z), evaluated from y=0y = 0 to y=zy = z, yielding: sin(2z)sin(z)\sin(2z) - \sin(z)
    • 0zcos(2y+z)dy\int_0^z \cos(2y+z) \, dy gives a similar result. Substituting u=2y+zu = 2y + z results in 12sin(2y+z)\frac{1}{2} \sin(2y+z), evaluated from y=0y = 0 to y=zy = z, yielding: 12[sin(3z)sin(z)]\frac{1}{2} [\sin(3z) - \sin(z)]

    Combining these, we get: (sin(2z)sin(z))12[sin(3z)sin(z)](\sin(2z) - \sin(z)) - \frac{1}{2} [\sin(3z) - \sin(z)]

  3. Final integral (with respect to zz): Finally, integrate this result with respect to zz: 0π2(sin(2z)sin(z)12[sin(3z)sin(z)])dz\int_0^{\frac{\pi}{2}} \left( \sin(2z) - \sin(z) - \frac{1}{2} [\sin(3z) - \sin(z)] \right) dz Breaking this up:

    • 0π2sin(2z)dz=12cos(2z)0π2=1\int_0^{\frac{\pi}{2}} \sin(2z) \, dz = -\frac{1}{2} \cos(2z) \Big|_0^{\frac{\pi}{2}} = 1
    • 0π2sin(z)dz=cos(z)0π2=2\int_0^{\frac{\pi}{2}} \sin(z) \, dz = -\cos(z) \Big|_0^{\frac{\pi}{2}} = 2
    • 0π2sin(3z)dz=13cos(3z)0π2=13\int_0^{\frac{\pi}{2}} \sin(3z) \, dz = -\frac{1}{3} \cos(3z) \Big|_0^{\frac{\pi}{2}} = \frac{1}{3}
    • 0π2sin(z)dz=2\int_0^{\frac{\pi}{2}} \sin(z) \, dz = 2, so 12×2=1\frac{1}{2} \times 2 = 1.

    Combining all these: 1212×(132)=1212×(53)1 - 2 - \frac{1}{2} \times \left( \frac{1}{3} - 2 \right) = 1 - 2 - \frac{1}{2} \times \left( -\frac{5}{3} \right) Simplifying: 1+56=16-1 + \frac{5}{6} = -\frac{1}{6}

Thus, the value of the triple integral is: 16\boxed{-\frac{1}{6}}

Would you like further details on any step or clarification? Here are 5 related questions to practice:

  1. How do you evaluate a triple integral in cylindrical coordinates?
  2. What is the Jacobian determinant for a change of variables in multiple integrals?
  3. How can you change the order of integration in a triple integral?
  4. What is the physical interpretation of a triple integral in real-world applications?
  5. Can you evaluate a triple integral using spherical coordinates for a given function?

Tip: Always check the limits of integration carefully, especially when changing variables or switching the order of integration.

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Math Problem Analysis

Mathematical Concepts

Multivariable Calculus
Triple Integration
Trigonometric Integrals

Formulas

Substitution method: \( u = x + y + z \)
Integral of sine: \( \int \sin(u) \, du = -\cos(u) + C \)

Theorems

Fundamental Theorem of Calculus
Change of Variables in Integration

Suitable Grade Level

Undergraduate (Calculus III or Advanced Calculus)