Determine the exact values of the following expressions.
Do NOT use decimals.
Type 'sqrt' if you need to use square root.
If a value is undefined, type 'undefined.'

$\tan (\frac{-7\pi}{2}) =$

$\cot (\frac{\pi}{6}) =$

$\sec (\frac{5\pi}{2}) =$

$\csc (\frac{2\pi}{3}) =$