what do the letters in pre-algebra mean?

Question

I dont understand the letters used in pre-algebra for example: x2 + y2=13 where y= 2

Answer 1

The letters such as x and y are technically speaking just symbols to represent a variable. They could be anything from a to z, and what they actually meant depends on the context of the question.

For example, in this question:

"Alisa bought x apples and y bananas.
How many fruits did she bought in total?"

x will mean the number of apple bought and y will mean the number of banana bought.

For x^2 + y^2 = 13, x and y just represent certain variables, and nothing more than that.