If the direction ratio of two lines are given by 3lm - 4ln + mn =

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 Multiple Choice QuestionsMultiple Choice Questions

731.

XOZ-plane divides the join of (2, 3, 1) and(6, 7, 1) in the ratio :

  • 3 : 7

  • 2 : 7

  • - 3 : 7

  • - 2 : 7


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732.

If the direction ratio of two lines are given by 3lm - 4ln + mn = 0 and l + 2m + 3n = 0, then the angle between the lines, is :

  • π6

  • π4

  • π3

  • π2


D.

π2

We have,3lm - 4ln + mn = 0    ... iand  l +2m +3n = 0   ...ii     From Eq.ii, l = -2m +3nUsing in Eq. i, we get      - 32m + 3nm + 42m + 3n + mn = 0     - 6m2 - 9mn + 8mn +12n2 +mn = 0                                     - 6m2 + 12n2  = 0Now, m2 = 2n2  m = ± 2nNow, m = 2n l = - 22n + 3n = - 22 + 3n l : m : n = - 3 + 22n : 2 n n                    = - 3 + 22: 2 : 1

Also, m = - 2n l = - - 22 + 3nl : m : n = - 3 + 22n : - 2 n . n             = - 3 - 22 : - 2 . 1If θ is the angle between the lines, thencosθ = l1l2 + m1m2 + n1n2l12 + m12  + n12 l22 + m22  + n22            =  3 + 223 - 22 + - 2 + 1 . 13 + 222 + 22  + 12 3 - 222 + - 22  + 12            = 9 - 8 - 2 + 19 + 8 + 122 + 2 + 19 + 8 - 122 + 2 + 1 = 0 cosθ  = 0  cosθ = cosπ2  θ = π2


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733.

A plane makes intercepts 3 and 4 respectively on Z-axis and X-axis. If it is parallel to Y-axis, then its equation is

  • 3x + 4z = 12

  • 3z + 4x = 12

  • 3y + 4z = 12

  • 3z + 4y = 12


734.

The equation of the plane passing through(1, 1, 1) and   (1, - 1, - 1) and perpendicular to 2x -y + z = 0 is :

  • 2x +5y +z + 8 = 0

  • x + y - z - 1 = 0

  • 2x + 5y + z + 4 = 0

  • x - y + z - 1 = 0


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735.

If 3i^ + 3j^ + 3k^, 3i^ + 3j^ + λk^ are coplaner, then λ is equal to

  • 1

  • 2

  • 3

  • 4


736.

If the direction ratio of two lines are given by l + m + n = 0, mn - 2ln + lm = 0, then the angle between the lines is

  • π4

  • π3

  • π2

  • 0


737.

If (2, - 1, 3) is the foot of the perpendicular drawn from the origin to the plane, then the equation of the plane is

  • 2x + y - 3z + 6 = 0

  • 2x - y + 3z - 14 = 0

  • 2x - y + 3z - 13 = 0

  • 2x + y + 3z - 10 = 0


738.

If the plane 3x - 2y - z - 18 = 0 meets the coordinate axes in A, B, C then the centroid of ABC is

  • (2, 3, - 6)

  • (2, - 3, 6)

  • (- 2, - 3, 6)

  • (2, - 3, - 6)


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739.

The direction cosines of the line passing through P(2, 3, - 1) and the origin are

  • 214, 314, 114

  • 214, - 314, 114

  • - 214, - 314, 114

  •  214, - 314, - 114


740.

If the direction cosines of two lines are such that l + m + n = 0, l2 + m2 - n2 = 0, then the angle between them is :

  • π

  • π3

  • π4

  • π6


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