The expression that does NOT represent 9+9+9+9+9+9+9 is 9 x 7.
Problem-Solving
The given expression 9+9+9+9+9+9+9 can be simplified by adding all the numbers together:
9+9+9+9+9+9+9 = 63
Therefore, the expression 63 represents 9+9+9+9+9+9+9.
However, if we multiply 9 by 7, we get:
9 x 7 = 63
Therefore, 9 x 7 represents the product of 9 and 7, not the sum of seven nines.