Question

Let $\vec{a}=\alpha \hat{i}+\hat{j}-\hat{k}$ and $\vec{b}=2 \hat{i}+\hat{j}-\alpha \hat{k}, \alpha>0$. If the projection of $\vec{a} \times \vec{b}$ on the vector $-\hat{ i }+2 \hat{ j }-2 \hat{ k }$ is $30$, then $\alpha$ is equal to

• A. $\frac{15}{2}$
• B. 8
• C. $\frac{13}{2}$
• D. 7

Answer 1

Answer: (D)

7

Answer 2

The correct option is (D): 7