How do I work these out?
2 answers:
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The step function is characteristic of the floor or ceiling functions, which map a real number to an integer. There's clearly a factor of 2, indicated by two units of y for every one unit of x.
The open and filled circles indicate, for example, f(1)=2, f(1.01)=4. That means we're rounding up, so we're using the ceiling function.
Answer: second choice