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The Cartesian equation of a line AB is: 2x-12=y+22=z-33. Find the direction cosines of a line parallel to line AB.

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Question

The Cartesian equation of a line AB is: `(2x - 1)/2 = (y + 2)/2 = (z - 3)/3`. Find the direction cosines of a line parallel to line AB.

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Solution

We have, `(2x - 1)/2 = (y + 2)/2 = (z - 3)/3`

The equation of line AB can be rewritten as `(x - 1/2)/6 = (y - (-2))/2 = (z - 3)/3`

Thus, direction ratios of the line parallel to AB are proportional to 6, 2, 3.

Hence, the direction cosines of the line parallel to AB are proportional to `6/sqrt(6^2 + 2^2 + 3^2), 2/sqrt(6^2 + 2^2 + 3^2), 3/sqrt(6^2 + 2^2 + 3^2)`

or `6/sqrt(49), 2/sqrt(49), 3/sqrt(49)`

or `6/7, 2/7, 3/7`

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2021-2022 (March) Term 2 - Delhi Set 3

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