Practicing Success
If $\vec{a} \times \vec{b}=\vec{c}$ and $\vec{b} \times \vec{c}=\vec{a}$ then |
$\vec{a} . \vec{c} \neq 0$ $ \vec{a} . \vec{c} \neq \vec{b} . \vec{c}$ $|\vec{a}|=|\vec{c}|$ none of these |
$|\vec{a}|=|\vec{c}|$ |
$\vec{a}(\vec{a} \times \vec{b})=\vec{a} . \vec{c}=0 $ Also $\vec{b}(\vec{a} \times \vec{b})=\vec{b} . \vec{c}=0$, and $\vec{b}(\vec{b} \times \vec{c})=\vec{a} . \vec{b}=0$ $\Rightarrow \vec{a}, \vec{b}, \vec{c}$ are mutually perpendicular vectors. $\Rightarrow |\vec{a} \times \vec{b}|=|\vec{a}||\vec{b}|=|\vec{c}|$ and $|\vec{b}||\vec{c}|=|\vec{a}| \Rightarrow|\vec{b}|=1 \Rightarrow|\vec{a}|=|\vec{c}|$ Hence (3) is correct answer. |