ACT Preparation / Unit 10 ACT 0905 short lesson, about 20 seconds
The Vertical Line Test
Captions available
The idea
A graph shows a function exactly when no vertical line crosses it more than once, since each crossing is an output for the same input.
In practice
A parabola opening up passes; a circle fails, because a vertical line through it hits twice.
Where people slip
The test checks for a function, not for one-to-one; that needs the horizontal test.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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