College Algebra / Unit 5 Alg 243 short lesson, about 20 seconds
The Horizontal Line Test
Captions available
The idea
The horizontal line test reads a graph for one-to-one: if any horizontal line crosses more than once, some output belongs to two inputs.
In practice
On y = x², the horizontal line y = 4 hits (2, 4) and (−2, 4) — a function, but not one-to-one.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
Builds on
- Nothing. This is a starting point.
Unlocks
- Nothing yet depends on this.
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