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Let L be the point (t, 2) and M be a point on the y-axis such that the slope of LM is −t. Then, the locus of the midpoint of LM is a parabola whose latus rectum is(a) 2(b) 1/2(c) 4(d) 1/4 |
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Answer» Correct option (b) 1/2 Explanation : Let M = (0, k) so that the slope of LM is 2 - k/t - 0 = -t ⇒ 2 - k = -t2 ....(1) Let (x, y) be the midpoint of LM. Therefore x = t/2 and y = 2 + k/2 Hence, from Eq. (1), we have 2y = 2 + k = 2 + (2 + t2) = 4 + t2 = 4 + 4x2 y = 2 + 2x2 x2 = 1/2(y - 2) Hence, the latus rectum is 1/2. |
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