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Vector Algebra

JEE Main 2024 (Online) 8th April Morning ShiftMCQMedium📈 Topic in 36% papers+4−1
Ques. 1JEE Main 2024, 8 April (Morning Shift)

The set of all , for which the vectors a = t i + 6 j - 3 k and b = t i - 2 j - 2 t k are inclined at an obtuse angle for all t R, is

  1. [0, 1)
  2. (- 43, 0 ]
  3. (-2, 0]
  4. (- 43, 1 )

Answer

(2) (- 43, 0 ]

Solution

For an obtuse angle, a b < 0 for all t:

a b = t2 - 12 + 6 t < 0 t R

= 0: -12 < 0 is always true, so = 0 is allowed

0: the quadratic is negative for all t only if < 0 and D < 0

D = 36 2 + 48 = 12 (3 + 4) < 0 - 43 < < 0

( a, b antiparallel would need = -3, outside this set)

(- 43, 0 ]

Answer: (2)

Keep practising — Vector Algebra

Ques. 2JEE Main 2024, 8 April (Morning Shift)

Let a = 9 i - 13 j + 25 k, b = 3 i + 7 j - 13 k and c = 17 i - 2 j + k be three given vectors. If r is a vector such that r a = ( b + c) a and r ( b - c) = 0, then |593 r + 67 a|2(593)2 is equal to .

Ques. 3JEE Main 2024, 8 April (Evening Shift)

Let a = 4 i - j + k, b = 11 i - j + k and c be a vector such that ( a + b) c = c (-2 a + 3 b). If (2 a + 3 b) c = 1670, then | c|2 is equal to:

  1. 1600
  2. 1618
  3. 1627
  4. 1609
Ques. 4JEE Main 2024, 8 April (Evening Shift)

Let a = i + 2 j + 3 k, b = 2 i + 3 j - 5 k and c = 3 i - j + k be three vectors. Let r be a unit vector along b + c. If r a = 3, then 3 is equal to:

  1. 21
  2. 25
  3. 27
  4. 30
Ques. 5JEE Main 2024, 6 April (Morning Shift)

If A(3, 1, -1), B ( 53, 73, 13 ), C(2, 2, 1) and D ( 103, 23, -13 ) are the vertices of a quadrilateral ABCD, then its area is

  1. 4 23
  2. 2 23
  3. 5 23
  4. 2 2
Ques. 6JEE Main 2024, 6 April (Morning Shift)

Let a = 2 i - 3 j + 4 k, b = 3 i + 4 j - 5 k and a vector c be such that a ( b + c ) + b c = i + 8 j + 13 k. If a c = 13, then (24 - b c ) is equal to .

Ques. 7JEE Main 2024, 6 April (Evening Shift)

Let a = 2 i + j - k, b = (( a ( i + j)) i) i. Then the square of the projection of a on b is:

  1. 13
  2. 15
  3. 2
  4. 23
Ques. 8JEE Main 2024, 6 April (Evening Shift)

Let a = 6 i + j - k and b = i + j. If c is a vector such that | c| 6, a c = 6| c|, | c - a| = 2 2 and the angle between a b and c is 60 , then |( a b) c| is equal to:

  1. 32 6
  2. 92(6 - 6)
  3. 92(6 + 6)
  4. 32 3
Ques. 9JEE Main 2024, 5 April (Morning Shift)

If A(1, -1, 2), B(5, 7, -6), C(3, 4, -10) and D(-1, -4, -2) are the vertices of a quadrilateral ABCD, then its area is :

  1. 24 7
  2. 48 7
  3. 24 29
  4. 12 29
Ques. 10JEE Main 2024, 5 April (Morning Shift)

Let a = i - 3 j + 7 k, b = 2 i - j + k and c be a vector such that ( a + 2 b) c = 3( c a). If a c = 130, then b c is equal to .

Ques. 11JEE Main 2024, 5 April (Evening Shift)

Let a = 2 i + 5 j - k, b = 2 i - 2 j + 2 k and c be three vectors such that ( c + i) ( a + b + i) = a ( c + i). If a c = -29, then c (-2 i + j + k) is equal to:

  1. 15
  2. 10
  3. 5
  4. 12

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