Q28 of 46 Page 215

The vectors -are and coplanar if

Given that,


Let


Now, are coplanar


if,


⇒ λ (λ2-1) -1(λ+2) +2(-1-2 λ)=0


⇒ λ3- λ –λ-2-2-4 λ=0


⇒ λ3- 6λ-4 =0


⇒ (λ+2)( λ2-2 λ-2)=0


⇒ λ = -2 and


⇒ λ = -2 and λ = 1±√3

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