Point P(a, b) is in the first quadrant. A circle of radius r, centre P and containing points in each quadrant is drawn. If AK is the area inside the circle in the Kth quadrant, K=1, 2, 3, 4, then A1-A2+A3-A4=
(a) ab (b) 2ab (c) 3ab (d) 4ab.
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