Give an example of a relation that is not a function and explain why it is not a function.
i do not understand how to do its algebra.

The desired example is this: x=y^2
Because for each x>0 we have two different possible y values which means it is not a function anymore. a function should only maximum 1 y value for each x value.

You can see the above relation has multiple possible values for y because if we take x=1 then y can be -1 or 1.