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A circle passes through origin and has its centre on the line y = x. If the circle cuts the circle x2 + y2 - 4x - 6y +10 = 0 orthogonally, then its equation is(A) x2 + y2 + 2x + 2y = 0(B) x2 + y2 + 2x - 2y = 0(C) x2 + y2 - 2x - 2y = 0(D) x2 + y2 - 2x - 2y = 0 |
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Answer» Correct option (D) x2 + y2 - 2x - 2y = 0 Explanation : Let S≡ x2 + y2 + 2gx + 2fy + c = 0 be the required circle which passes through (0, 0). This implies that c = 0 ....(1) The circle has the centre on the line y = x which implies that -g = -f ....(2) g = f The circle cuts the circle x2 + y2 - 4x - 6y + 10 = 0 orthogonally implies that 2(g)(-2) +2f(-3) = (-3) = c + 10 -4g -6f = c + 10 .....(3) From Eqs. (1) – (3), we have g = f = -1 and c = 0. Therefore S ≡ x2 + y2 - 2x - 2y = 0 |
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