In the equation y=2x+3, 2 & 3 are called constants & the x & y are called this because they can change
For example, ax^2 +by + c = 0 is a function (quadratic function) but... [DOC] [TLE] Algebra - Simple Equations | SkillsYouNeed [PAR] You can use any letter you like, although x and y are commonly used to ... A letter 
used to substitute for a number in algebra is called a variable, because it ...