An equation is a mathematical sentence that contains a __________________: equal sign. What is a variable: letter. A math sentence that does not contain an equal sign: Expression. A math sentence containing an equal sign. : Equation. When a letter and a number are right next to each other, it means they are _____________. : Multiplying . The number before a variable is the _____: coefficient. A letter that represents a number is called a _____: variable. A number with no variable attached is called a _____: constant