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Problem 1352
1352
The diagram shows the circle with equation \((x-2)^2 + y^2 = 8\). The chord \(AB\) of the circle intersects the positive \(y\)-axis at \(A\) and is parallel to the \(x\)-axis.
(a) Find, by calculation, the coordinates of \(A\) and \(B\).
(b) Find the volume of revolution when the shaded segment, bounded by the circle and the chord \(AB\), is rotated through 360° about the \(x\)-axis.
Solution
(a) To find the coordinates of \(A\), substitute \(x = 0\) into the circle equation \((x-2)^2 + y^2 = 8\):
\((-2)^2 + y^2 = 8\)
\(4 + y^2 = 8\)
\(y^2 = 4\)
\(y = 2\) (since \(A\) is on the positive \(y\)-axis)
Thus, \(A = (0, 2)\).
For \(B\), since \(AB\) is parallel to the \(x\)-axis, \(y = 2\). Substitute \(y = 2\) into the circle equation:
\((x-2)^2 + 4 = 8\)
\((x-2)^2 = 4\)
\(x-2 = \pm 2\)
\(x = 4\) (since \(B\) is on the right side of the circle)
Thus, \(B = (4, 2)\).
(b) The volume of revolution is found by integrating the area of the segment rotated about the \(x\)-axis: