What is the slope of the x-axis?
2 answers:
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1) 
2)
Here, the variable
can assume any value, and usually an inequality presented like this has as a stand-in for all real numbers. If we really wanted to make that fact clear, we could write the two inequalities like this:
Formally, you'd read
as " is an element of the set of real numbers," which is a fancy way of saying that can be any real number.
2)
Here, the variable
Formally, you'd read