Te angle between two diagonals of a cube is from Mathematics Thr

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 Multiple Choice QuestionsMultiple Choice Questions

631.

The line x - 23 = y - 34 = z - 45 is parallel to the plane

  • 2x + 3y + 4z = 0

  • 3x + 4y + 5z = 7

  • 2x + y - 2z = 0

  • x + y + z = 2


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632.

Te angle between two diagonals of a cube is

  • cos-113

  • 30°

  • cos-113

  • 45°


A.

cos-113

Let edge of a cube be 1 unit.

The diagonals of a cube are OA and BC

So, DR's of diagonals OA are (1, 1, 1) and BC are (0 - 1, 1, 1), i.e., (- 1, 1, 1).

Now, angle between diagonals,cosθ = 1- 1 + 11 + 1112 + 12 + 1212 + 12 + 12          = 112 + 12 + 1212 + 12 + 12          = 133 = 13 θ = cos-113


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633.

Lines x - 21 = y - 31 = z - 4- k and x - 1k = y - 42 = z - 51 are coplanar, if

  • k = 2

  • k = 0

  • k = 3

  • k = - 1


634.

If a = i^ + 2j^ + 2k^, b = 5 and the angle between a and b is π6, then the area of the triangle formed by these two vectors as two sides is

  • 154

  • 152

  • 1532

  • 15


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635.

If direction cosines of a vector of magnitude 3 are 23, - 93, 23, then vector is

  • i^ - 2j^ + 2k^

  • 2i^ + j^ + 2k^

  • i^ + 2j^ + 2k^

  • None of these


636.

Equation of line passing through the point (2, 3, 1) and parallel to the line of intersection of the planes x - 2y - z + 5 = 0 and x + y + 3z = 6 is

  • x - 25 = y - 34 = z - 13

  • x - 25 = y - 3- 4 = z - 13

  • x - 24 = y - 33 = z - 12

  • x - 2- 5 = y - 3- 4 = z - 13


637.

Foot of perpendicular drawn from the origin to the plane 2x - 3y + 4z = 29 is

  • (7, - 1, 3)

  • (5, - 1, 4)

  • (5, - 2, 3)

  • (2, - 3, 4)


638.

Suppose a + b + c = 0, a = 3, b = 5, c = 7, then the angle between a and b is

  • π

  • π2

  • π3

  • π4


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639.

The vector equation of the plane, which is at a distance of 314, from the origin and the normal from the origin is 2i^ - 3j^ + k^ is

  • r . 2i^ - 3j^ + k^ = 3

  • r . i^ + j^ + k^ = 9

  • r . i^ + 2j^ = 3

  • r . 2i^ + k^ = 3


640.

Find the coordinates of the foot of the perpendicular drawn from the origin to the plane 5y + 8 = 0.

  • 0, - 185, 2

  • 0, 85, 2

  • 825, 0, 0

  • 0, - 85, 0


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