Answer: B) one-to-one
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Step-by-step explanation:
It is a function because it passes the vertical line test. We cannot draw a single vertical line through more than one point on the red curve. Any x input leads to exactly one and only one y output.
A similar test is the horizontal line test. We cannot draw a single horizontal line through more than one point on the red curve, so this red curve passes the horizontal line test. Each y is only paired with one x value only. This helps set up an inverse function.
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In short:
If the curve passes the vertical line test, then we have a function
If the curve passes the horizontal line test, then it is one-to-one.