If a→ and c→ are unit vector and |b→|=4 and the angle between a→ and c→ is cos−1(1/4) and b→−2c→=λa→ the value of λ is
3,- 4
14,34
-3, 4
-14,34
b→−2c→=λa→ or b→=2c→+λa→ or |b→|2=|2c→+λa→|2
⇒ 16=4|c→|2+λ2|a→|2+4λa→⋅c→ =4+λ2+4λ14 or λ2+λ−12=0 or λ=3,−4