• Quick retrieval from earlier learning (Decide whether a relation is a function). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Is this relation a function? {(−2, 2), (2, 5), (8, −6), (6, 2), (4, 8)} (Yes / No) → YesPrompt: In a function, each input (x) has exactly one output (y).
2. Which set of ordered pairs is a function? ({(6, 5), (0, 5), (−2, 1), (4, 3)} / {(−3, −3), (6, 6), (−2, −3), (−2, −1)} / {(2, 6), (5, 3), (−4, 3), (2, 8)} / {(0, 6), (−2, 4), (3, −1), (0, 7)}) → {(6, 5), (0, 5), (−2, 1), (4, 3)}Prompt: Check the first coordinates in each set.
3. Is this relation a function? {(−4, 5), (0, −4), (−5, −4), (7, 3), (6, 7)} (Yes / No) → YesPrompt: In a function, each input (x) has exactly one output (y).

• Show a "think of a number" puzzle and ask the class to work out the starting number.
• Share the objective: Find the domain and range of a set of ordered pairs. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: R = {(9, 0), (7, −5), (3, −4), (−1, 1)}. What is the domain of R?
• Step 1: {−1, 3, 7, 9}
• Answer: {−1, 3, 7, 9}
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. R = {(2, −4), (4, −2), (6, 1), (9, 6)}. What is the domain of R? ({2, 4, 6} / {2, 4, 6, 9} / {−4, −2, 1, 6} / {−4, −2, 1, 2, 4, 6, 9}) → {2, 4, 6, 9}Prompt: Domain: all the inputs (first numbers). Range: all the outputs (second numbers).
2. The function f = {(4, −2), (−3, 6), (−4, −3), (9, −2), (3, 6), (0, −3)}. How many different values are in its range? → 3Prompt: The range is the set of outputs.

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 6 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. The function f = {(4, 1), (−1, 1), (3, 0), (−3, 0), (0, −4), (8, −4)}. How many different values are in its range? → 3Prompt: The range is the set of outputs.
2. R = {(4, −5), (5, 0), (−3, 2), (6, 8)}. What is the range of R? ({−5, 0, 2} / {−5, 0, 2, 8} / {−5, −3, 0, 2, 4, 5, 6, 8} / {−3, 4, 5, 6}) → {−5, 0, 2, 8}Prompt: Domain: all the inputs (first numbers). Range: all the outputs (second numbers).

Free online practice with hints and printable worksheets for this skill: eurekami.com/math/grade-9.