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The region between the curve

y=sec x,0 <= x <= (pi)/(4)
and the 
x-axis is revolved about the 
x-axis to generate a solid.
Find the exact value of its volume.

The region between the curve\newliney=secx,0xπ4 y=\sec x, 0 \leq x \leq \frac{\pi}{4} \newlineand the x x -axis is revolved about the x x -axis to generate a solid.\newlineFind the exact value of its volume.

Full solution

Q. The region between the curve\newliney=secx,0xπ4 y=\sec x, 0 \leq x \leq \frac{\pi}{4} \newlineand the x x -axis is revolved about the x x -axis to generate a solid.\newlineFind the exact value of its volume.
  1. Disk Method Integration: To find the volume of the solid, we use the disk method, which involves integrating the area of circular disks along the x-axis from x=0x=0 to x=π4x=\frac{\pi}{4}.
  2. Area of Disk Calculation: The area of a disk at a particular xx is given by A(x)=π[sec(x)]2A(x) = \pi[\sec(x)]^2, since the radius of the disk is the yy-value of the function, which is sec(x)\sec(x).
  3. Volume Integral Calculation: The volume VV is the integral of A(x)A(x) from x=0x=0 to x=π4x=\frac{\pi}{4}. So, V=0π4π[sec(x)]2dxV = \int_{0}^{\frac{\pi}{4}} \pi[\sec(x)]^2 \, dx.
  4. Integral Evaluation: Now we calculate the integral: V=π0π4sec2(x)dxV = \pi\int_{0}^{\frac{\pi}{4}} \sec^2(x) \, dx.
  5. Final Volume Calculation: The antiderivative of sec2(x)\sec^2(x) is tan(x)\tan(x), so we evaluate tan(x)\tan(x) from 00 to (π)/(4)(\pi)/(4).
  6. Final Volume Calculation: The antiderivative of sec2(x)\sec^2(x) is tan(x)\tan(x), so we evaluate tan(x)\tan(x) from 00 to π4\frac{\pi}{4}.Evaluating the antiderivative at the bounds gives us V=π[tan(π4)tan(0)]V = \pi[\tan(\frac{\pi}{4}) - \tan(0)].
  7. Final Volume Calculation: The antiderivative of sec2(x)\sec^2(x) is tan(x)\tan(x), so we evaluate tan(x)\tan(x) from 00 to (π)/(4)(\pi)/(4). Evaluating the antiderivative at the bounds gives us V=π[tan((π)/(4))tan(0)]V = \pi[\tan((\pi)/(4)) - \tan(0)]. Since tan((π)/(4))=1\tan((\pi)/(4)) = 1 and tan(0)=0\tan(0) = 0, we have V=π[10]V = \pi[1 - 0].
  8. Final Volume Calculation: The antiderivative of sec2(x)\sec^2(x) is tan(x)\tan(x), so we evaluate tan(x)\tan(x) from 00 to (π)/(4)(\pi)/(4). Evaluating the antiderivative at the bounds gives us V=π[tan((π)/(4))tan(0)]V = \pi[\tan((\pi)/(4)) - \tan(0)]. Since tan((π)/(4))=1\tan((\pi)/(4)) = 1 and tan(0)=0\tan(0) = 0, we have V=π[10]V = \pi[1 - 0]. Therefore, the volume V=πV = \pi cubic units.

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