An equation is a statement that two mathematical expressions are equal. An expression is a combination of numbers, variables, and operations.

A linear equation is an equation with one variable and one or two terms, such as y = 2x + 1. A quadratic equation is an equation with one variable and three terms, such as y = ax2 + bx + c. 
 

A function is a mathematical relationship between two sets of values. A function takes an input value, performs a calculation on it, and returns an output value. For example, y = 2x + 1 is a function that takes an input value x, multiplies it by 2, and adds 1 to the result.