#### How do you evaluate functions?

**The same way that you substitute values into equations!**

What is the value of $$ x $$ given the equation $$ y = 2x $$ when $$ x = 5 $$?

Substitute '5' in for x :

The one new aspect of function notation is the emphasis on input and output .

Example 2What is the value of $$ x $$ given the equation $$ y = x-5 $$ when $$ x = 7 $$?