What is the angle between $\hat{i} + \hat{j}$ and $\hat{j} + \hat{k}$?

Explanation

1. 01

   $\cos \theta = \frac{\vec{a} \cdot \vec{b}}{\lvert \vec{a} \rvert \lvert \vec{b} \rvert} = \frac{1}{\sqrt{2}\sqrt{2}} = \frac{1}{2}$.

2. 02

   $\theta = \frac{\pi}{3}$.