How many minimum number of coplanar vectors having different magnitudes can be added to give zero resultant

The magnitudes of vectors $\vec A,\,\vec B$ and $\vec C$ are $3, 4$ and $5$ units respectively. If $\vec A + \vec B = \vec C$, the angle between $\vec A$ and $\vec B$ is

If two vectors $\vec{A}$ and $\vec{B}$ having equal magnitude $\mathrm{R}$ are inclined at an angle $\theta$, then

Three vectors $\overrightarrow{\mathrm{OP}}, \overrightarrow{\mathrm{OQ}}$ and $\overrightarrow{\mathrm{OR}}$ each of magnitude $A$ are acting as shown in figure. The resultant of the three vectors is $A \sqrt{x}$. The value of $x$ is. . . . . . . . .

What vector must be added to the two vectors $\hat i - 2\hat j + 2\hat k$ and $2\hat i + \hat j - \hat k,$ so that the resultant may be a unit vector along $X-$axis

If $\overrightarrow R$ is the resultant vector of two vectors $\overrightarrow A $ and $\overrightarrow B $, then  $\overrightarrow {\left| R \right|} \,...\,\overrightarrow {\left| A \right|} \, + \,\overrightarrow {\left| B \right|} $.