###### Example1.10

As of 2016, One World Trade Center in New York City is the nations tallest building, at 1776 feet. If an algebra book is dropped from the top of One World Trade Center, its height above the ground after \(t\) seconds is given by the equation

Thus, after \(1\) second the books height is

After \(2\) seconds its height is

For this function, \(t\) is the input variable and \(h\) is the output variable. For any value of \(t\text{,}\) a unique value of \(h\) can be determined from the equation for \(h\text{.}\) We say that \(h\) *is a function of* \(t\text{.}\)