Question 192370
A horizontal line says "No matter what {{{x}}} is, {{{y}}} always
stays the same. A way to write it is {{{y = c}}} where {{{c}}} is
a constant value.
An example would be {{{y}}} is the number of items in a safe
which is buried deep under ground and no one knows where
it is. {{{x}}} is the number of days that pass with the number
of items not changing.
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A vertical line says "No matter what {{{y}}} is, {{{x}}} is always
the same. It can be written {{{x = c}}}
An example would be {{{y}}} is all the possible temperatures
in the universe and {{{x}}} is an instant in time