Question

Let \(\vec a,\vec b,\vec c\) be three vectors satisfying \(\vec a\times\vec b=\vec a\times\vec c\), \(|\vec a|=|\vec c|=1\), \(|\vec b|=4\) and \(|\vec b\times\vec c|=\sqrt{15}\). If \(\vec b-2\vec c=\lambda \vec a\), then \(\lambda\) equals

• A. \(1\)
• B. \(-1\)
• C. \(2\)
• D. \(-4\)

Hint:

If \(\vec a\times\vec x=0\), then \(\vec x\parallel\vec a\).

Answer 1

The Correct Option is B