Expressions vs. Equations

An expression like 3x + 5 is a recipe for computing a value once you know x. An equation like 3x + 5 = 20 is a statement that two things are equal — and it challenges you to find which x makes it true. The distinction matters: expressions compute, equations constrain.

Simplifying expressions means combining like terms. 4x + 2x = 6x because four groups of x plus two more groups make six groups. But 4x + 2y cannot be simplified — x and y are different variables, like adding apples and oranges.