We add the unit vectors $\hat{i}, \hat{j}$ and $\hat{k}$. Is it a unit vector? How can we convert the sum to a unit vector?

The magnitude of $\overrightarrow{a}+\overrightarrow{c}$ is equal to the magnitude of $\overrightarrow{b}+\overrightarrow{d}$.

The four vectors $\overrightarrow{a}, \overrightarrow{b}, \overrightarrow{c}$ and $\overrightarrow{d}$ can be represented by the four sides of a rectangle taken in the same order.

The magnitude of $\overrightarrow{a}$ can never be greater than the sum of the magnitudes of $\overrightarrow{b}, \overrightarrow{c}$ and $\overrightarrow{d}$.