If a→=i^+2j^−k^,b→=2i^−j^+k^ and c→=λi^+j^+2k^are coplanar, then the value of λ-4
Vector a→=i^+2j^−k^,b→=2i^−j^+k^ ,c→=λi^+j^+2k^ are coplanar
⇒ 12−12−11λ12=0 or λ−3+2(−5)=0 or λ=13