Curve C is a circle with radius 2 and center at the origin with equation . Line L has the equation . The diagram below shows the shaded region A which is enclosed between C and L.

- (a)
Use the substitution to show that the area of region A can be written in the expression , where , and are exact constants to be determined. Hence evaluate this area exactly.
- (b)
The region B is bounded by the curve C, the line L and the line . Find the volume generated when region B is rotated through radians about the y-axis. Give your answer to two decimal places.
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Worked solution
7(a)
1. Set up the area integral as the difference between the area under the curve and the area under the line.
From the given intersection points and , the limits of integration are and .
2. Evaluate the integral for the line to find the exact constant $c$.
3. Apply the substitution $x = 2\sin\theta$ to the integral for the curve to find $a$ and $b$.
Change of limits:
When ,
When ,
Substitute into the integral:
Comparing this with , we have exact constants and .
4. Integrate $4\cos^2\theta$ using the double angle identity.
Using the identity :
5. Evaluate the definite integral and subtract $c$ to find the exact area.
Finally, subtract to find the exact area:
, ,
Area
7(b)
1. Express the boundary equations in terms of $y$ and determine the limits of integration along the $y$-axis.
The outer boundary is the vertical line . The inner boundary is defined by the curve from to , and the line from to .
2. Set up the volume integrals using the washer method for the two separate sections of Region B.
3. Evaluate the definite integral for the first volume segment ($V_1$).
4. Evaluate the definite integral for the second volume segment ($V_2$).
5. Sum the volumes and convert to a decimal value rounded to two decimal places.
8.46
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