An equation can be true or false. An example of a true equation is $7+1=4 \boldcdot 2$. An example of a false equation is $7+1=9$. 

An equation can have a letter in it to represent a value, for example, $u+1=8$. This equation is false if $u$ is 3, because $3+1$ does not equal 8. This equation is true if $u$ is 7, because $7+1=8$.

A letter in an equation that represents an unknown value is called a variable. In $u+1=8$, the variable is $u$. A number that can be used in place of the variable that makes the equation true is called a solution to the equation. In $u+1=8$, the solution is 7.

When a number is written next to a variable, it means the number and the variable are being multiplied. For example, $7x=21$ means the same thing as $7 \boldcdot x = 21$. A number written next to a variable is called a coefficient. If no coefficient is written, the coefficient is 1. For example, in the equation $p+3=5$, the coefficient of $p$ is 1.