The value of $ i^3 + i^4 + i^5 $+ .. + $i^{93}$ is:
If $ |\vec{a}| = 5 $, $ |\vec{b}| = 8 $, $ |\vec{a} - \vec{b}| = 7 $, find the angle between $ \vec{a} $ and $ \vec{b} $.