What a Function Is Worksheets, Grade 8 (8.F.A.1) – Free PDF + Answer Key

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PDFs print on US Letter paper. Free for classroom and home use.

Key idea

Each input gets exactly one output. Repeated outputs are fine; a repeated input with different outputs is not.

Is this a function? (2,7) (3,7) (4,7)
Is this a function? (5,1) (6,2) (5,9)
Write the definition of a function in your own words.
Explain the difference between “each input has one output” and “each output has one input”.

Said no because the outputs are all different, or because no rule was given. Neither is the test.
Said yes by scanning the outputs (1, 2, 4 are all different) instead of the inputs. The test is on the INPUT side.
Agreed with her. This is the central misconception of the topic: the two sentences are nearly identical in words and completely different in meaning. Reading both aloud back to back is the fastest correction.

The answer key explains each one, so you can tell what a wrong answer means.

Teach with the slides (about 15 minutes), or watch the video together.
Practice with the worksheet. Questions climb from fluency to application to reasoning.
Check understanding with the exit ticket, and send the homework home.
Mark with the answer key — each answer shows the steps and the most likely mistake.