If a variable 'y' depends upon a variable 'x' in such a way that each value of 'x' determines exactly one value of 'y', then we say that
If a variable 'y' depends upon a variable 'x' in such a way that each value of 'x' determines exactly one value of 'y', then we say that
Explanation
If each value of 'x' determines exactly one value of 'y', then:
The variable y depends on x
For every input x, there is a unique output y
This is the definition of a function in mathematics.