Practice question · Multiple choice
A relation passing the vertical line test is a function; one passing the horizontal test as well is invertible. Why does invertibility need the second test?
Hints
- Reflect the graph in and apply the vertical test to the result.
- Ask what becomes after the swap.
Show the answer
D. Because the inverse swaps inputs and outputs
Why
Reflecting in turns the horizontal test into the vertical one. This is why needs its domain restricted before a square-root inverse exists.
Practise Functions, domains, and representations
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