Aspire Faculty ID #16567 · Topic: NIMCET 2008 · Just now
NIMCET 2008

Let $\vec A=2\vec i+\vec j-2\vec k$ and $\vec B=\vec i+\vec j$. If $\vec C$ is a vector such that $\vec A\cdot\vec C=|\vec C|$, $|\vec C-\vec A|=2\sqrt2$ and the angle between $\vec A\times\vec B$ and $\vec C$ is $30^\circ$, then $|(\vec A\times\vec B)\times\vec C|$ is equal to

Solution

$|\vec A\times\vec B|=\sqrt{(2,-2,1)\cdot(2,-2,1)}=3$ Using $|(\vec A\times\vec B)\times\vec C|=|\vec A\times\vec B||\vec C|\sin30^\circ$ From given conditions, $|\vec C|=1$ Hence $=3\times1\times\dfrac12=\dfrac32$ Answer: $\boxed{\dfrac32}$

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