Chapter 9: Problem 27
Use the fact that \(r^{2}+h^{2}=\ell^{2}\) in a right circular cone (Theorem 9.3.6). A triangle has sides that measure \(15 \mathrm{cm}, 20 \mathrm{cm},\) and \(25 \mathrm{cm} .\) Find the exact volume of the solid of revolution formed when the triangle is revolved about the side of length \(25 \mathrm{cm}\) (HINT: The altitude to the 25 -cm side has length \(12 \mathrm{cm}\).)
Short Answer
Step by step solution
Recognize the Shape Formed
Identify Cone Dimensions
Apply Pythagorean Theorem
Solve for the Radius
Apply the Volume Formula for a Cone
Calculate the Volume
Final Calculation
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Right Circular Cone
A right circular cone gets its name because its apex aligns directly above the center of its circular base, forming a right angle between its height and the base.
Understanding this symmetry can be helpful when solving related problems, such as calculating volume or surface area.
- The base of the cone is circular.
- The axis of the cone is perpendicular to the base.
- The apex is directly above the center of the base.
Pythagorean Theorem
Expressed as a formula, it is \(a^2 + b^2 = c^2\), where \(c\) is the hypotenuse, and \(a\) and \(b\) are the other two sides.
- This theorem is often used to calculate the unknown side of a right triangle when the other two sides are known.
- It is essential in solving problems related to right circular cones, as it helps find missing dimensions such as the radius or height.
Volume of a Cone
\[ V = \frac{1}{3} \pi r^2 h \]
Where \(V\) is the volume, \(r\) is the radius of the base, and \(h\) is the height.
- The formula shows that the volume of a cone is one-third of the volume of a cylinder with the same base and height.
- This makes sense intuitively, as a cone is essentially a tapering pyramid.
- To compute the volume accurately, you need to ensure you have precise measurements for the radius and height.
Mathematical Problem Solving
Here’s how to efficiently solve a solid of revolution problem using a triangle, as exemplified by the right circular cone formation:
- Understand the geometric shapes involved and how they transform, such as a triangle forming a cone when revolved.
- Identify all the known quantities and figure out what is missing. Relate these using geometric theorems like the Pythagorean Theorem.
- Apply the correct formulas for the problem, such as the volume formula for a cone.
- Perform precise calculations to arrive at the solution.