Vectors `5hati+yhatj+hatk,2hati+2hatj-2hatk` and `-hati+2hatj+2hatk` are coplaner then find the value of y.

Answer

A, B

Explanation

For (A) : Required component `=((vec(a)-vec(b)).(vec(a)+vec(b)))/(|vec(a)+vec(b)|)=(a^(2)-b^(2))/sqrt(a^(2)+b^(2)+2ab cos 60^(@))=(a^(2)-b^(2))/sqrt(a^(2)+b^(2)+ab)`
For (B) : `vec(a)+2vec(b)+vec(a)-vec(b)=2vec(a)+vec(b)` which lies in the plane of `vec(a)` and `vec(b)`
`rArr` resultant is perpendicular to `vec(a)xxvec(b)`