Applications of Integrals · Volume
Disk Method
Volume of revolution about the x-axis when there is no gap between the curve and the axis. Each cross-section is a disk with radius f(x).
Variables
| Symbol | Name | Unit |
|---|---|---|
| a | Left bound | — |
| b | Right bound | — |
Worked examples
Find the volume when y = √x is revolved about the x-axis on [0, 4].
- V = π ∫₀⁴ (√x)² dx = π ∫₀⁴ x dx = π[x²/2]₀⁴ = π(8) = 8π
Answer: 8π ≈ 25.13
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