हिंदी

Find the shortest distance between the lines whose vector equations are r→=(1-t)i^+(t-2)j^+(3-2t)k^ and r→=(s+1)i^+(2s+1)k^.

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प्रश्न

Find the shortest distance between the lines whose vector equations are `vecr = (1-t)hati + (t - 2)hatj + (3 -2t)hatk` and `vecr = (s+1)hati + (2s + 1)hatk`.

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उत्तर

Equations of given lines

`vecr = (1 - t)hati + (t - 2)hatj + (3 - 2t)hatk` 

or `vecr = hati - 2hatj + 3hatk + t (-hati + hatj - 2hatk)`

and `vecr = (s + 1)hati + (2s - 1)hatj + (2s + 1)hatk`

or `vecr = hati - hatj + hatk + s (hati + 2hatj - 2hatk)`

Comparing the above equations with `vecr = vec(a_1) + λvec(b_1)` and `vecr = vec(a_2) +µvec(b_2)`,

`vec(a_1) = hati - 2hatj + 3hatk, vec(b_1) = - hati + hatj - 2hatk`

and `vec(a_2) = hati - hatj - hatk, vec(b_2) = hati + 2hatj - 2hatk`

∴ `vec(a_2)  - vec(a_1) = (hati - hatj - hatk) - (hati - 2hatj + 3hatk) = hatj - 4hatk`

`vec(b_1) xx vec(b_2) = (- hati + hatj - 2hatk) xx (hati + 2hatj - 2hatk)`

= `|(hati, hatj, hatk), (-1, 1, -2), (1, 2, -2)|`

= `(-2 + 4)hati - (2 + 2)hatj + (-2 -1)hatk`

= `2hati - 4hati - 3hatk`

∴ `|vec(b_1) xx vec(b_2)|`

= `sqrt((2)^2 + (-4)^2 + (-3)^2)`

= `sqrt(4 + 16 + 9)`

= `sqrt29`

∴ Required minimum distance d = `|((vec(a_2) - vec(a_1)). (vec(b_1) xx vec(b_2)))/|vec(b_1) xx vec(b_2)||`

= `|((hatj - 4hatk). (2hati - 4hatj - 3hatk))/sqrt29|`

= `|(-4 + 12)/sqrt29|`

= `8/sqrt29`

Hence, the minimum distance between the given lines is `8/sqrt29`.

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अध्याय 11: Three Dimensional Geometry - Exercise 11.2 [पृष्ठ ४७८]

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एनसीईआरटी Mathematics Part 1 and 2 [English] Class 12
अध्याय 11 Three Dimensional Geometry
Exercise 11.2 | Q 17 | पृष्ठ ४७८

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