# Exercises: Comprehension check
## Exercise 1
To declare these functions in the REPL, you need to prepend them with **let**.

`let half x = x / 2`

`let square x = x * x`

## Excercise 2
In the REPL:

`let foo x = 3.14 * (x * x)`

## Excercise 3
In the REPL:

`let bar x = pi * (x * x)`