Common symbols at a glance
A few signs come up again and again: ≠ means not equal, ≈ means approximately equal, and ± shows a value that can go either way. √ is the square root, ∞ stands for infinity and π is the ratio of a circle’s circumference to its diameter. In calculus, ∑ adds up a series, ∫ marks an integral and ∂ indicates a partial derivative.
Sets, logic and number systems
Set theory uses ∈ for “is an element of”, ⊂ for “is a subset of”, and ∪ and ∩ for union and intersection, while ∅ is the empty set. Logic adds ∀ (for all), ∃ (there exists), ¬ (not), ∧ (and) and ∨ (or). Double-struck letters like ℕ, ℤ, ℚ, ℝ and ℂ name the natural, integer, rational, real and complex numbers.