rule & function

In Mathematics, a rule is a set way to perform an operation or solve a problem.

eg BEDMAS

eg Angles in a triangle sum up to 180°.

An algebraic rule is a mathematical expression that relates variables and is written as an equation.

eg Circumference of a circle: C = π d

eg Linear graph: y = mx + c

A function is a rule that follows a specific idea; for every input (x value) there is only ONE output (y-value).

Example 1

This is a function because for any input (x value) you select, there is only one output (y-value)

When x = 3, y = 2 ✕ 3 + 4 = 10

When x = 5, y = 2 ✕ 5 + 4 = 14

Example 2

This is NOT a function because for any input (x value) you select, there are two outputs (y-values)

When x = 9, y = 3 and -3 (as  3 ✕ 3 = 9 AND -3 ✕ -3 = 9)