An **expression** is a group of mathematical symbols representing a number or a quantity.

$3a$

$2x + 8$

$a^2 - 89$

An **equation** is a mathematical statement indicating that two expressions are equal. The equation is not inherently true or false, it’s only a proposition; it’s truth value has to be calculated. Solving an equation means finding the value(s) that make the equation true. If there are none, the equation is false.

$2x + 1 = 7$

$8(x + 3) = 64$

$4y + 8 = 2y$

A **formula** is an equation expressing a relationship between constant and variable quantities. Often, the equation in the formula is a means to finding the value of one quantity (often a single variable) in terms of another or other quantities.

$E = mc^2$

$A = \pi r^2$

$P = 2(L + W)$