• math
• pi
• **

# Solution: Calculations

In order to have the math operation work properly we had to put the addition in parentheses. Just as you would in math class.

examples/basics/rectangle_solution.py
```width = 23
height = 17
area = width * height
print("The area is ", area)    # 391
circumference = 2 * (width + height)
print("The circumference is ", circumference)    # 80

```
In order to calculate the area and the circumference of a circle we need to have PI so we created a variable called pi and put in 3.14 which is a very rough estimation. You might want to have a more exact value of PI.

examples/basics/circle_solution.py
```r = 7
pi = 3.14
print("The area is ", r * r * pi)           # 153.86
print("The circumference is ", 2 * r * pi)  # 43.96

```
Python has lots of modules (aka. libraries, aka. extensions), extra code that you can import and start using. For example it has a module called math that provides all kinds of math-related functions and attributes.

A function does something, an attribute just hold some value. More about this later.

Specifically it has an attribute you can call math.pi with the value 3.141592653589793. A much better proximation of PI.

In the following solution we used that.

• The documentation of the math module.

examples/basics/circle_math_solution.py
```import math

r = 7
print("The area is ", r * r * math.pi)           # 153.9380400258998
print("The circumference is ", 2 * r * math.pi)  # 43.982297150257104

```
The expression r * r might also bothered your eyes. Well don't worry in Python there is an operator to express exponential values It is the double star: . This is how we can use it to say r-square: r 2.

examples/basics/circle_power_solution.py
```r = 7
pi = 3.14
print("The area is ", r ** 2 * pi)           # 153.86
print("The circumference is ", 2 * r * pi)  # 43.96

```
I don't have much to say about the calculator. I think it is quite straight forward.

examples/basics/calc_solution.py
```a = 3
b = 2

print(a+b)   # 5
print(a-b)   # 1
print(a*b)   # 6
print(a/b)   # 1.5

```