Comparison:
  $\sim$ Similar to
  $\approx$ Almost equal, rounded
  $\ne$ Unequal to
  $<$ Less than
  $>$ Greater than
  $\le$ Less than or equal to
  $\ge$ Greater than or equal to

Logic:
  $\wedge$ Logical And
  $\vee$ Logical Or
  $\neg$ Logical Not
  $\to$ If, then (conditional)
  $\leftrightarrow$ Exactly when (biconditional)

Sets:
  $\in$ Element of
  $\notin$ No element of
  $\cap$ Intersection
  $\cup$ Union

Angles:
  $°$ Degree
  $\prime$ Degree minute
  $″$ Degree second
  $\alpha$ Alpha
  $\beta$ Beta
  $\gamma$ Gamma

Other symbols:
  $\Delta$ Delta, difference
  $\pi$ Pi
  $\mu$ Micro
  $\pm$ Plus-minus
  $\infty$ Infinity