The teacher is explaining to his students the remarkable fact that twice gives the same answer as two plus two.
Although 2 is the only integer that has this property there are many pairs of numbers that can replace TO Y B in the equations that are to the right of the board.
Can you discover a pair like that? Of course, they can be fractions but your product must be equal to the sum.
There are infinite pairs of numbers that have the same sum and product. We can get all we want as follows.
If we call TO to one of the two numbers, the other can always be obtained by dividing TO between A - 1.
For example: 3 times 1.5 is equal to 4.5 and 3 plus 1.5 is also equal to 4.5.