Key Idea: Value of a Function

The value of a function is the output you get when you substitute a number into the function’s variable.

General Rule:

• Substitute the given input (usually $x$) into the function:

  f(x)=expression with x

• Plug in the value of $x$ to solve for the output {$y$ or f(x)}.

Why this matters for the SAT:

Finding function values is a common algebra skill on the SAT.
It helps you evaluate expressions, interpret function notation, and solve problems involving inputs and outputs quickly.