Why It Matters: Set Theory and Logic
Why understand set theory and logic applications?
![Tic-Tac-Toe game at a playground made of big yellow cylinders with black X's and O's printed on them.](https://s3-us-west-2.amazonaws.com/courses-images/wp-content/uploads/sites/1141/2017/03/28210931/tictactoe-225x300.jpg)
![Tic-tac-toe game with two X's and two O's.](https://s3-us-west-2.amazonaws.com/courses-images/wp-content/uploads/sites/1141/2017/03/28212148/tictactoe1-300x290.png)
- It takes three in a row to win the game.
- I cannot make three in a row no matter where I play on this turn.
- If it were my opponent’s turn, then she could make three in a row by putting an O in the upper left corner.
- If I don’t put my X in the upper left corner, then my opponent will have the opportunity to play there.
- Therefore, I must put an X in the upper left corner.
![Tic-Tac-Toe example, continued, with red X in the upper left corner.](https://s3-us-west-2.amazonaws.com/courses-images/wp-content/uploads/sites/1141/2017/03/28212213/tictactoe2-300x294.png)