Math Problem Statement

Determine whether the statement is true: Let E be the 3-D region: E: x² + y² + z² < 4, z ≥ 1. Then, E has cylindrical description 0 ≤ r ≤ 1, 0 ≤ 0 ≤ 2π, 1 ≤ x ≤ √4-r2.

Solution

To determine if the statement is true, we need to check if the region EE described in spherical coordinates is equivalent to the cylindrical description given.

Region EE in Spherical Coordinates

The region EE is described by:

  1. x2+y2+z2<4x^2 + y^2 + z^2 < 4: This describes a sphere of radius 2 centered at the origin.
  2. z1z \geq 1: This describes a region above the plane z=1z = 1.

So, EE is the volume inside the sphere of radius 2, and above the plane z=1z = 1.

Cylindrical Description Analysis

The cylindrical coordinates are:

  • rr: the radial distance from the z-axis in the xy-plane,
  • θ\theta: the angle from the positive x-axis in the xy-plane,
  • zz: the height along the z-axis.

The cylindrical description given is:

  1. 0r10 \leq r \leq 1
  2. 0θ2π0 \leq \theta \leq 2\pi
  3. 1x4r21 \leq x \leq \sqrt{4 - r^2}

Conversion and Comparison

  • The bound 0r10 \leq r \leq 1 describes a cylinder with radius 1.
  • The bound 0θ2π0 \leq \theta \leq 2\pi covers the full circular range around the z-axis.
  • The bound 1x4r21 \leq x \leq \sqrt{4 - r^2} is not appropriate for cylindrical coordinates because xx should be replaced with zz in cylindrical coordinates. Moreover, this condition seems misplaced as it compares xx with an expression involving rr, which doesn't fit the cylindrical coordinate description.

The correct way to describe EE in cylindrical coordinates should involve the zz coordinate, not xx. Additionally, rr should range from 0 to 4z2\sqrt{4 - z^2} because it depends on zz for the sphere boundary.

Conclusion

The provided cylindrical description is incorrect. It should use zz instead of xx and include proper bounds on rr and zz to match the sphere and plane conditions.

The statement is false.


Would you like more details on cylindrical coordinates or the conversion process?

Here are 5 questions you might be interested in:

  1. How do you convert between spherical and cylindrical coordinates?
  2. Can you explain the intersection of a sphere and a plane in 3D space?
  3. How do you describe a sphere in cylindrical coordinates?
  4. What are common mistakes in converting between coordinate systems?
  5. How does the z-bound affect the radial bound in cylindrical coordinates?

Tip: Always double-check the coordinate system and ensure variables correspond correctly to avoid mix-ups like using xx in cylindrical descriptions.