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Determine the equation of the circle which touches the line y = x at the origin and bisects the circumference of the circle x2 + y2 + 2y − 3 = 0. |
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Answer» Let S ≡ x2 + y2 + 2gx + 2fy + c = 0 be the required circle. It passes through (0, 0). This implies c = 0. Now S = 0 touches the line x - y = 0. Therefore If S = 0 bisects the circumference of S' ≡ x2 + y2 + 2y − 3 = 0, then S - S' = 0 passes through the centre (0, 1) of S' = 0. This implies that 2gx - 2(g + 1)y + 3 = 0 passes through (0, -1 ) (:. f = -g) ⇒ 0 -2(g + 1)(-1) + 3 = 0 ⇒2g = -5 = -2f Therefore, S ≡ x2 + y2 - 5x + 5y = 0 |
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