The problem asks us to find the volume generated by rotating the area bounded by the axes and the curve $y = cos(x)$ between $x=0$ to $x=\pi$ about the $x$-axis. We need to determine which of the provided options matches the calculated volume. There is an apparent typo in the prompt. Rather than through 2, it should read 'through $2\pi$'.

AnalysisCalculusVolume of RevolutionIntegrationTrigonometryDefinite IntegralsDisk Method
2025/4/25

1. Problem Description

The problem asks us to find the volume generated by rotating the area bounded by the axes and the curve y=cos(x)y = cos(x) between x=0x=0 to x=πx=\pi about the xx-axis. We need to determine which of the provided options matches the calculated volume. There is an apparent typo in the prompt. Rather than through 2, it should read 'through 2π2\pi'.

2. Solution Steps

We use the disk method to find the volume of the solid of revolution. The volume is given by the integral:
V=πab[f(x)]2dxV = \pi \int_{a}^{b} [f(x)]^2 dx
In our case, f(x)=cos(x)f(x) = cos(x), a=0a=0, and b=πb=\pi. Therefore, the volume is:
V=π0πcos2(x)dxV = \pi \int_{0}^{\pi} cos^2(x) dx
We can rewrite cos2(x)cos^2(x) using the identity:
cos2(x)=1+cos(2x)2cos^2(x) = \frac{1 + cos(2x)}{2}
So the integral becomes:
V=π0π1+cos(2x)2dxV = \pi \int_{0}^{\pi} \frac{1 + cos(2x)}{2} dx
V=π20π(1+cos(2x))dxV = \frac{\pi}{2} \int_{0}^{\pi} (1 + cos(2x)) dx
V=π2[x+12sin(2x)]0πV = \frac{\pi}{2} [x + \frac{1}{2}sin(2x)]_{0}^{\pi}
V=π2[(π+12sin(2π))(0+12sin(0))]V = \frac{\pi}{2} [(\pi + \frac{1}{2}sin(2\pi)) - (0 + \frac{1}{2}sin(0))]
V=π2[π+000]V = \frac{\pi}{2} [\pi + 0 - 0 - 0]
V=π2πV = \frac{\pi}{2} * \pi
V=π22V = \frac{\pi^2}{2}
None of the options matches π22\frac{\pi^2}{2}.
If instead, we consider the area bounded by the x-axis and the curve y=cos(x)y = cos(x) between x=0x=0 and x=π2x=\frac{\pi}{2}, we would have:
V=π0π2cos2(x)dxV = \pi \int_{0}^{\frac{\pi}{2}} cos^2(x) dx
V=π20π2(1+cos(2x))dxV = \frac{\pi}{2} \int_{0}^{\frac{\pi}{2}} (1 + cos(2x)) dx
V=π2[x+12sin(2x)]0π2V = \frac{\pi}{2} [x + \frac{1}{2}sin(2x)]_{0}^{\frac{\pi}{2}}
V=π2[(π2+12sin(π))(0+12sin(0))]V = \frac{\pi}{2} [(\frac{\pi}{2} + \frac{1}{2}sin(\pi)) - (0 + \frac{1}{2}sin(0))]
V=π2[π2+000]V = \frac{\pi}{2} [\frac{\pi}{2} + 0 - 0 - 0]
V=π2π2V = \frac{\pi}{2} * \frac{\pi}{2}
V=π24V = \frac{\pi^2}{4}

3. Final Answer

If the limits were 0 to π/2\pi/2 then the answer is (D) 14π2\frac{1}{4}\pi^2

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