If a= (2x+y )i+3j+9k and b=2i+j- (x-y )k are two collinear vectors, then x^3+27y^3=

Question

Accepted Answer

Correct answer: D. (d) Given: a= (2x+y )i+3j+9k b=2i+j- (x-y )k ∵ a and b are co-linear vectors ∴ 2x+y2= 31= 9- (x-y ) ⇒ 2x+y2= 31 ⇒2x+y=6 … (i ) and 31= 9y-x ⇒y-x=3…..(ii) Solving eqns. (i) and (ii), we get x=1 and y=4 Now, x^3+27y^3=1+27 64=1729.

$If a = (2 x + y) i + 3 j + 9 k and b = 2 i + j - (x - y) k are two collinear vectors, then x^{3} + 27 y^{3} =$

Solution

More Vector Algebra PYQs