Find the distance between the line r(t) = a + tb and the origin given that?

a = j (j being the unit vector (0,1,0) and b = i – j where i is the unit vector (1,0,0) ). Therefore i – j = (1,-1,0).

Please show all steps in arriving at the answer which is: 1 divided by the square root of 2. Thanks!

1 Answer

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  • r(t) = <0, 1, 0> + t<1, -1, 0>

    ||r(t)||² = t² + (1 – t)²

    which is also the square of the distance of r(t) for a certain t from the origin.

    Minimize to find the distance.

    d||r(t)||²/dt = 2t – 2(1 – t) = 0

    t = 1/2

    ||r(1/2)||² = (1/2)² + (1 – 1/2)²

    ||r(1/2)||² = 1/2

    ||r(1/2)|| = 1/sqrt(2)

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