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If a point P with x -coordinate 7 lies on the line joining the points A (1, 2, 3) and B (4, 6, 8) then the coordinates of the point P are

  • A.(7,10, -13)
  • B.(7,-10, 13)
  • C.(7,10, 12)
  • D.(7,10, 13)
  • E.(7,10, 15)

Answer: D

P is (7, 10, 13).

The direction from A(1, 2, 3) to B(4, 6, 8) is (3, 4, 5), so points of the line are \((1 + 3t, 2 + 4t, 3 + 5t)\). For x = 7, \(1 + 3t = 7\) gives t = 2:

\[ (1 + 6, 2 + 8, 3 + 10) = (7, 10, 13) \]

So P lies beyond B, with AP = 2AB. The options with -10 or -13 have the wrong signs, and (7, 10, 12) and (7, 10, 15) have the right y but a z that does not lie on the line.

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