The diagram below shows a region bounded by the curve and the line . Find the volume of solid formed when is rotated through four right angles about the x-axis.

- ((a))
The diagram below shows a region bounded by the curve and the line . Find the volume of solid formed when is rotated through four right angles about the x-axis.
- ((b))
- ((i))
Show that where is an arbitrary constant.
- ((ii))
A curve is defined by the parametric equations
\Gamma\Gammax=1$.
- ((i))
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Worked solution
8((a))
1. Find the points of intersection between the curve and the line.
Substitute the line equation into the curve's equation:
When , . When , .
Thus, the intersections are and .
2. Express the curve with $y$ as the subject and identify the upper and lower branches to determine the boundaries of the region.
Making the subject of the curve's equation:
The parabola opens to the right with its vertex at .
The inner boundary of the region (closer to the -axis, hence smaller radius of revolution) is the upper branch:
The outer boundary (further from the -axis, hence larger radius) is split into two sections:
- The lower branch of the curve: for
- The line: for
3. Set up the definite integrals for the volume of the solid generated when the region $R$ is rotated $360^\circ$ about the $x$-axis.
The volume is found using the washer/disc method, requiring us to split the region at based on the outer boundaries:
Substituting the functions:
4. Evaluate the integrals (analytically or via a graphing calculator) to find the exact volume.
Simplifying the integrands:
Evaluating the definite integrals:
Total volume:
8((b))((i))
1. Set up the first application of integration by parts.
Let .
Using the integration by parts formula :
Let and .
Then and .
2. Apply the integration by parts formula to obtain a new integral.
3. Apply integration by parts a second time to the new integral.
For , let and .
Then and .
4. Substitute back to form an equation in terms of $I$ and solve.
Substitute this result back into the earlier equation for :
(where is an arbitrary constant of integration.)
8((b))((ii))
1. Find the value of parameter $t$ and coordinates at the $y$-axis.
At the -axis, .
When , .
The point of intersection with the -axis is .
2. Find the gradient of the curve at $t=0$.
Using parametric differentiation:
At :
3. Determine the equation of the tangent at the $y$-axis.
Using the point and gradient :
4. Set up the area integral for the region.
The region is bounded by the curve, the tangent, and the line . The integration bounds for are from to .
5. Evaluate the area using parametric substitution and the result from (b)(i).
For the curve integral, substitute . As goes from to , goes from to .
Using the integration result from (b)(i):
Now evaluate the tangent line's definite integral:
Therefore, the exact area is:
\frac{1}{5}e^{-\pi} + \frac{2}{5}
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