numbers and algebraic expressions
logic, sets, intervals
function and its properties
limits of sequences and functions
derivative and integral of functions
elements of statistics
Absolute value removes minus of a negative number. Zero and positive number stay without changes. Examples: |-3| = 3, |0| = 0, |4| = 4, |-5| = 5, |1/2| = |1/2|. Absolute value is always positive or equals zero.