Question

Let $\vec{a}$ and $\vec{b}$ be two vectors, Let $|\vec{a}|=1,|\vec{b}|=4$ and $\vec{a} \cdot \vec{b}=2$ If $\vec{c}=(2 \vec{a} \times \vec{b})-3 \vec{b}$, then the value of $\vec{b} \cdot \vec{c}$ is

• A. $-60$
• B. $-48$
• C. $-84$
• D. $-24$

Answer 1

Answer: (B)

$-48$

Answer 2

c=(2a×b)−3b
b⋅c=b⋅(2a×b)−3b⋅b
=−3∣b∣2
=−48
So, the correct answer is (B) : -48