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# If $\overrightarrow {a}=-\overrightarrow {i}+\overrightarrow {j}+2\overrightarrow {k} , \overrightarrow {b}=2\overrightarrow {i}-\overrightarrow {j}-\overrightarrow {k}$ and $\overrightarrow {c}=-2 \overrightarrow {i}+\overrightarrow {j}+3 \overrightarrow {k},$ then the angle between $2 \overrightarrow {a}-\overrightarrow {c}$ and $\overrightarrow {a}+\overrightarrow {b}$ is :

$\begin {array} {1 1} (1)\;\frac{\pi}{4} & \quad (2)\;\frac{\pi}{3} \\ (3)\;\frac{\pi}{2} & \quad (4)\;\frac{3 \pi}{2} \end {array}$

Can you answer this question?

$(2)\;\frac{\pi}{3}$
answered Nov 7, 2013 by