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Tangents are drawn from any point on the circle x2 + y2 + R2 to the circle x2 + y2 + r2. If the line joining the points of intersection of these tangents with the first circle also touches the second, then R:r is(A) 2:1 (B) 1:2(C) 3:1(D) √2 : 1 |
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Answer» Let P(x1, y1) be a point on x2 + y2 = R2. Suppose the tangents from point P to the circle x2 + y2 = r2 meet the circle with radius R in A and B such that AB touches the circle with centre r. Thus, for ΔPAB, x2 + y2 = R2 is the circumcircle and x2 + y2 = r2 is the incircle and hence the circumcentre and incentre are the same. Therefore, the triangle is equilateral so that R= 2r |
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