NCERT Solutions for class 12 Maths | Chapter 10 - Vector Algebra

(1) The distance of the point (- 3, 4, 5) from the origin
[A] 50
[B] 5√2
[C] 6
[D] None of these
Answer: 5√2
(2) If are coplanar then P =
[A] 6
[B] -6
[C] 2
[D] -2
Answer: 6

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(3) If |a + b| = |a – b|, then angle between a and b is (a ≠ 0, b ≠ 0)
[A] π/3
[B] π/6
[C] π/4
[D] π/2
Answer: π/2
(4) a, b, c are three vectors, such that a + b + c = 0, |a|= 1, |b|= 2, |c|= 3, then a.b + b.c + c is equal to
[A] 0
[B] -7
[C] 7
[D] 1
Answer: -7
(5) If |a – b| = |a| = |b| = 1, then the angle between a and b is
[A] π/3
[B] 3π/4
[C] π/2
[D] 0
Answer: π/3
(6) If |a| = |b| = 1 and |a + b| = √3, then the value of (3a – 4b).(2a + 5b) is
[A] -21
[B] −21/2
[C] 21
[D] 21/2
Answer: −21/2
(7) Let a, b and c be vectors with magnitudes 3, 4 and 5 respectively and a + b + c = 0, then the values of a.b + b.c + c.a is
[A] 47
[B] 25
[C] 50
[D] -25
Answer: -25
(8) The number of vectors of unit length perpendicular to the vectors a = and
[A] one
[B] two
[C] 4
[D] infinite
Answer: two
(9) If |a| = 4 and -3 ≤ λ ≤ 2, then the range of |λa| is
[A] [0, 8]
[B] [-12, 8]
[C] [0, 12]
[D] [8, 12]
Answer: [8, 12]
(10) If a, b, c are unit vectors such that a + b + c = 0, then the value of a.b + b.c + c.a is
[A] 1
[B] 3
[C] −3/2
[D] None of these
Answer: −3/2
(11) The vectors are coplanar if
[A] λ = -2
[B] λ = 0
[C] λ = 1
[D] λ = -1
Answer: λ = -2
(12) The vectors from origin to the points A and B are a = and b = respectively then the area of triangle OAB is
[A] 340
[B] √25
[C] √229
[D] 1/2 √229
Answer: 1/2 √229
(13) The vectors are the side of a ΔABC. The length of the median through A is
[A] √18
[B] √72
[C] √33
[D] √288
Answer: √33
(14) If |a|= 5, |b|= 13 and |a × b|= 25, find a.b
[A] ±10
[B] ±40
[C] ±60
[D] ±25
Answer: ±60
(15) If |a × b| = 4 and |a.b| = 2, then |a|2 |b|2 is equal to
[A] 2
[B] 6
[C] 8
[D] 20
Answer: 20
(16) |a × b|2 + |a.b|2 = 144 and |a| = 4, then |b| is equal to
[A] 12
[B] 3
[C] 8
[D] 4
Answer: 3
(17) If AB × AC = then the are of ΔABC is
[A] 3 sq. units
[B] 4 sq. units
[C] 16 sq. units
[D] 9 sq. units
Answer: 3 sq. units
(18) If
[A] 0
[B] -1
[C] 1
[D] 2
Answer: -1
(19) If
[A] 5
[B] 10
[C] 14
[D] 16
Answer: 16
(20) The scalar product of
[A] 10
[B] -10
[C] 15
[D] -15
Answer: -10

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