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CBuilderMathematics· about 30 min· fundamentals that rarely change· verified 2026-09-20· EN

Functions and coordinate systems

Be able to read and draw a function as a graph, interpret the slope and the y-intercept in y = kx + m, and understand that a function is a rule that gives exactly one output per input.

Practise in Mattegrafen ↗ · Samband och förändring

Prerequisites

Intuition

A function is a machine: put a number in, get a number out. f(x) = 2x + 1 gives f(0) = 1, f(1) = 3, f(2) = 5. The same input always gives the same answer — that is the whole point.

Draw the pairs (x, f(x)) as points in a coordinate system and you get a picture of the function. For 2x + 1 it comes out as a straight line.

Formal

The straight line y = kx + m:

  • k is the slope: how much y goes up when x goes up by 1.
  • m is where the line crosses the y-axis (the value when x = 0).

From two points: k = (y₂ − y₁) / (x₂ − x₁). From (1, 3) and (3, 7): k = 4/2 = 2, and m = 3 − 2·1 = 1.

Why does AI care? A model that predicts one number from another is a function, and the simplest model is exactly a straight line. To "train" it means to find k and m.

Mastery means

  • Calculates y for a given x in a linear function
  • Reads k and m off a graph or a table

Sign in to do the exercises and build your mastery up.

Sources

All the sources and licences