Math Problem Statement

How to find limit here

Using triple integral, find the volume bounded above by the sphere x^2 + y^2 + z^2 = a^2 and below by the cone x^2 + y^2 = z^2.

Solution

To solve the problem using triple integrals and determine the volume bounded by the given cone and sphere, we need to establish the correct limits for integration.

Step 1: Understand the geometry

  1. Cone equation: x2+y2=z2x^2 + y^2 = z^2
    This is a cone symmetric about the zz-axis, with its vertex at the origin.
  2. Sphere equation: x2+y2+z2=a2x^2 + y^2 + z^2 = a^2
    This is a sphere centered at the origin with radius aa.

Step 2: Intersection of the cone and sphere

To find the intersection curve, substitute x2+y2=z2x^2 + y^2 = z^2 (from the cone) into x2+y2+z2=a2x^2 + y^2 + z^2 = a^2 (from the sphere): z2+z2=a22z2=a2z2=a22z=±a2z^2 + z^2 = a^2 \quad \Rightarrow \quad 2z^2 = a^2 \quad \Rightarrow \quad z^2 = \frac{a^2}{2} \quad \Rightarrow \quad z = \pm\frac{a}{\sqrt{2}} Thus, the cone intersects the sphere at z=a2z = \frac{a}{\sqrt{2}} and z=a2z = -\frac{a}{\sqrt{2}}.

Step 3: Convert to spherical coordinates

To simplify the volume computation, use spherical coordinates: x=ρsinϕcosθ,y=ρsinϕsinθ,z=ρcosϕ,x = \rho \sin\phi \cos\theta, \quad y = \rho \sin\phi \sin\theta, \quad z = \rho \cos\phi, where:

  • ρ\rho is the radial distance,
  • ϕ\phi is the angle from the positive zz-axis (0ϕπ0 \leq \phi \leq \pi),
  • θ\theta is the azimuthal angle (0θ<2π0 \leq \theta < 2\pi).

The volume element in spherical coordinates is: dV=ρ2sinϕdρdϕdθ.dV = \rho^2 \sin\phi \, d\rho \, d\phi \, d\theta.

Step 4: Integration limits

  • ρ\rho: From the cone (ρ=zcosϕ=ρcosϕcosϕ\rho = \frac{z}{\cos\phi} = \frac{\rho\cos\phi}{\cos\phi}) to the sphere (ρ=a\rho = a).
  • ϕ\phi: From 00 to π4\frac{\pi}{4} (since the cone forms an angle of ϕ=π4\phi = \frac{\pi}{4} with the zz-axis).
  • θ\theta: From 00 to 2π2\pi (full rotation around the zz-axis).

Step 5: Triple integral setup

The volume is given by: V=02π0π4ρ2aρ2sinϕdρdϕdθ.V = \int_0^{2\pi} \int_0^{\frac{\pi}{4}} \int_{\frac{\rho}{\sqrt{2}}}^a \rho^2 \sin\phi \, d\rho \, d\phi \, d\theta.

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Math Problem Analysis

Mathematical Concepts

Triple Integrals
Spherical Coordinates
Volume Calculation

Formulas

Volume element in spherical coordinates: dV = ρ^2 sinφ dρ dφ dθ
Equations of the cone: x^2 + y^2 = z^2
Equations of the sphere: x^2 + y^2 + z^2 = a^2

Theorems

Integration using spherical coordinates

Suitable Grade Level

Undergraduate (Calculus Level)