The Vertical Line Test
This video presents the same text shown beside it, spoken and on screen. It adds nothing the text does not say.
State
The vertical line test reads a graph: if any vertical line crosses the graph more than once, the graph is not a function.
Show
The graph of x = y² contains (4, 2) and (4, −2); the vertical line x = 4 hits both, so one input claims two outputs.
Builds on
- Nothing — this is a starting point.
Unlocks
- Nothing yet depends on this.