The value of p so that vectors `(2hati - hatj +),( hati +2hatj-3hatk)` and `(3hati + phatj + 5hatk)` are coplaner should be:

Options

A. 16
B. -4
C. 4
D. -8

Answer

B

Explanation

For coplanar vectors,
`vecA. vecB xx vecC =0`
`|{:(2,-1,1),(1,2,-3),(3,p,5):}|`
`2(10 +3p) +1(5 +9)+ 1(p-6)=0`
`20 + 6p +14 + p-6 =0`
`7p+ 28 =0`
`p= - 4`