owlking299

Hello Guest!

A rectangle can be made with 2 vertical dots and 2 horizontals.

For the 2 vertical dots there are 5 to choose from. 

that is choosing 2 dots from 5 or 5 choose 2. 

Now applying the same logic, we also need to choose 2 horizontal dots.

There are 5 dots to choose from. so we have 5 choose 2 

5 choose 2 is 10. there are 10 choices for horizontal and 10 choices for vertical.  10x10=100 choices for a rectangle

Ohh that makes more sense. I never thought about using a more abstract algebra or proving its strictly increasing.  Thank you! 

I used algebra and got the inverse but how can i prove that it is an inverse without graphing it?