World 1 · Functions & Limits · 6 minWhat is a function?
Inputs, outputs and rules
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A function is a rule that turns each input into exactly one output. Feed it a number x, and it hands back a number f(x). That is the whole idea — a reliable machine: same input in, same output out, every time.
We picture a function as a graph: the horizontal axis is the input x, the vertical axis is the output y = f(x). The height of the curve above a point tells you the output there. Reading a graph is reading the rule.
Check yourself
A function assigns each input…
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