$ABC$ is an equilateral triangle. Length of each side is $a$ and centroid is point $O$. Find $\overrightarrow{A B}+\overrightarrow{B C}+\overrightarrow{C A}=.......$
$0$
$1$
$2$
$3$
If $| A + B |=| A |+| B |$ the angle between $\overrightarrow A $and $\overrightarrow B $ is ....... $^o$
If the sum of two unit vectors is a unit vector, then magnitude of difference is
If two vectors $\vec{A}$ and $\vec{B}$ having equal magnitude $\mathrm{R}$ are inclined at an angle $\theta$, then