Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
Most Important Selected Qs for JEE AdvancedMathematicsVector Algebra

Let a , b and c be three unit vectors such that | a + b + c |= 3 and ( a b ) ( b c )+( b c ) ( c a )+( c a ) ( a b )= . Which of the following are CORRECT ?

Options

  1. AThe maximum value of is 0
  2. BIf is maximum then the volume of parallelepiped determined by a , b and c is 3
  3. CIf is maximum then the value of |(2 a +3 b +4 c ) ( a b +5 b c +6 c a )| is 32 .
  4. DNone of these

Correct answer

C. If is maximum then the value of |(2 a +3 b +4 c ) ( a b +5 b c +6 c a )| is 32 .

Step-by-step solution

aligned & ( a b ) ( b c )=( b c )( a b )- a c & ( b c ) ( c a )=( a c )( b c )- a b & ( c a ) ( a b )=( a b )( a c )- b c aligned Given that aligned & | a + b + c |= 3 ( a + b + c ) ( a + b + c )=3 a b + b c + c a =0 & =( a b ) ( b c )+( b c )( c a )+( c a )( a b )- a b - b c - c a & =( a b ) ( b c )+( b c )( c a )+( c a )( a b ) & 0[ since , x+y+z=0, x y+y z+ xx 0] & _ =0 only when a b = b c = a c =0 & a b , b c and c a & (2 a +3 ~b +4 c ) ( a b +5 ~b c +6 c a ) & =10 a ( b c )+18 ~b ( c a )+4 c ( a b )=32 aligned

Practice Vector Algebra on Quantrex Academy →

More from Vector Algebra

Let a , b be two vectors, and let P, Q and R be the points with position vectors a , b and a + b , respectively, with respect to the origin O . If | a + b | = 21 , | a - b | = 3 , 2026Let a = 4 i - j + 3 k , b = 10 i + 2 j - k and a vector c be such that 2( a b ) + 3( b c ) = 0 . If a c = 15 , then c ( i + j -3 k ) is equal to: 2026Let a = 2 i + 3 j + 3 k and b = 6 i + 3 j + 3 k . Then the square of the area of the triangle with adjacent sides determined by the vectors (2 a + 3 b ) and ( a - b ) is : 2026If a = i + j + k , b = j - k and c be three vectors such that a c = b and a c = 3 , then c ( a - 2 b ) is equal to _______. 2026Let O be the origin, OP = a and OQ = b . If R is the point on OP such that OP = 5 OR , and M is the point such that OQ = 5 RM , then PM is equal to : 2026Let a = 7 i + j - k and b = j + 2 k . If r is a vector such that r a + a b = 0 and r a = 0 , then |3 r |^2 is equal to: 2026Let u and v be unit vectors inclined at an acute angle such that | u v |= 3 2 . If A = u + v +( u v ) , then is equal to: 2026Let a_k = ( _k) i + j and b_k = i - ( _k) j , where _k = 2^ k-1 2^n + 1 , for some n N , n > 5 . Then the value of _ k=1 ^ n | a_k |^2 _ k=1 ^ n | b_k |^2 is _____. 2026 Full Vector Algebra list All Most Important Selected Qs for JEE Advanced PYQs