ACT Preparation / Unit 10 ACT 0906 short lesson, about 20 seconds
One-to-One and the Horizontal Line Test
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The idea
A function is one-to-one when each output comes from only one input. Its graph passes the horizontal line test: no horizontal line crosses it more than once.
In practice
f(x) = 2x + 1 is one-to-one; f(x) = x² is not, since f(3) = f(−3) = 9.
Where people slip
Only one-to-one functions have inverse functions.
Your place on the trail
Every lesson rests on earlier ones and opens later ones. Tap any to jump.
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