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Vector Algebra · Question 35

JEE Main 2025 (Online) 2nd April Evening ShiftMCQMedium📈 Topic in 52% papers+4−1
1

Let a = 2 i - 3 j + k, b = 3 i + 2 j + 5 k and a vector c be such that ( a - c) b = -18 i - 3 j + 12 k and a c = 3. If b c = d, then | a d| is equal to :

  1. 15
  2. 18
  3. 12
  4. 9

Answer

(1) 15

Solution

( a - c) b = a b - c b = a b + b c

a b = vmatrix i & j & k \ 2 & -3 & 1 \ 3 & 2 & 5 vmatrix = -17 i - 7 j + 13 k

d = b c = (-18 i - 3 j + 12 k) - (-17 i - 7 j + 13 k)

= - i + 4 j - k

(Check: b d = -3 + 8 - 5 = 0, as it must be.)

a d = 2(-1) + (-3)(4) + 1(-1) = -15

| a d| = 15

Answer: (1)

JEE Main 2025 (Online) 2nd April Evening Shift

Keep practising — Vector Algebra

2

Let a = 2 i - j + 3 k, b = 3 i - 5 j + k and c be a vector such that a c = c b and ( a + c) ( b + c) = 168. Then the maximum value of | c|2 is :

  1. 77
  2. 154
  3. 308
  4. 462
JEE Main 2025 (Online) 29th January Morning Shift
3

Let a = i + j + k, b = 2 i + 2 j + k and d = a b. If c is a vector such that a c = | c|, | c - 2 a|2 = 8 and the angle between d and c is 4, then |10 - 3 b c| + | d c|2 is equal to .

JEE Main 2025 (Online) 28th January Morning Shift
4

If the components of a = i + j + k along and perpendicular to b = 3 i + j - k respectively, are 1611(3 i + j - k) and 111(-4 i - 5 j - 17 k), then 2 + 2 + 2 is equal to:

  1. 16
  2. 23
  3. 26
  4. 18
JEE Main 2025 (Online) 28th January Evening Shift
5

Let A, B, C be three points in xy-plane, whose position vectors are given by 3 i + j, i + 3 j and a i + (1 - a) j respectively with respect to the origin O. If the distance of the point C from the line bisecting the angle between the vectors OA and OB is 9 2, then the sum of all the possible values of a is:

  1. 2
  2. 0
  3. 92
  4. 1
JEE Main 2025 (Online) 28th January Evening Shift

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