Domain and Range

The domain is every input a function uses; the range is every output it produces. Two bars on the graph — one along the bottom, one up the side — worked through a weight-over-years example and a temperature-over-a-day example.

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A function connects inputs to outputs. Domain and range are just the names for those two collections — every input you used, and every output you got back.

Definitions Two bars on the graph

The domain is the complete set of input values used. The range is the set of output values those inputs produced.

Picture it as two bars on the graph: one running along the bottom marking every input covered — that’s the domain — and one running up the side marking every output reached — that’s the range.

Example Weight over five years
domain — 5 years range — 60–80 kg
A person’s weight is tracked for five years. The five-year period is the domain — it contains every time value in the study. The weight wanders between and kg, so is the range.
Example Temperature over one day
domain — 1 day range — 25–30°
Temperature is recorded throughout a single day. Every time in that day is the domain. The readings vary from to degrees Celsius, so is the range.
Summary
  1. The domain is the complete set of input values used.
  2. The range is the set of output values those inputs produced.
  3. Weight over five years: domain is the 5-year period, range is kg.
  4. Temperature over one day: domain is every time in the day, range is degrees.