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Question 1

Let $$ABC$$ be a right-angled triangle with $$\angle ABC = 90^\circ$$, $$BD = 2a + 2$$, $$DC = 3a - 3$$, $$BE = 2a + 1$$ and $$EA = 4a + 1$$, where $$D$$ is the mid-point of side $$BC$$ and $$E$$ is a point on side $$AB$$. The area of the semicircle with diameter $$AC$$ is ______.

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Since $$D$$ is the mid-point of $$BC$$ we get $$2a + 2 = 3a - 3$$, so $$a = 5$$ and $$BD = DC = 12$$, giving $$BC = 24$$. Also $$AB = BE + EA = 11 + 21 = 32$$, so $$AC = \sqrt{24^2 + 32^2} = \sqrt{1600} = 40$$. The semicircle on $$AC$$ has radius 20, so its area is $$\frac{1}{2}\pi (20)^2 = 200\pi$$.

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