What is the minimum number of non-zero vectors in different planes that can be added to give a zero resultant?

State the important condition for the addition of vectors.

If $0.5 \hat{i} + 0.8 \hat{j} + c \hat{k}$ is a unit vector,then $c$ is

The resultant of two vectors $\vec{A}$ and $\vec{B}$ makes an angle $\alpha$ with $\vec{A}$ and an angle $\beta$ with $\vec{B}$. Which of the following is true?

The vectors $\overrightarrow{A}$ and $\overrightarrow{B}$ lie in a plane. Another vector $\overrightarrow{C}$ lies outside this plane. The resultant $\overrightarrow{R} = \overrightarrow{A} + \overrightarrow{B} + \overrightarrow{C}$ of these three vectors:

Two vectors of same magnitude act at a point. Twice the product of the magnitudes of two vectors is equal to the square of the magnitude of their resultant. The angle between the two vectors is (in $^{\circ}$)