• 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? {(−1, 1), (−2, 4), (−6, 6), (−1, 4), (−5, 8)} (Yes / No) → NoPrompt: In a function, each input (x) has exactly one output (y).
2. Which set of ordered pairs is a function? ({(−2, 5), (1, 3), (0, 6), (−2, 4)} / {(3, 3), (6, −3), (−4, −1), (1, 6)} / {(4, 5), (2, −3), (0, −3), (2, −4)} / {(3, 0), (1, −2), (5, 0), (5, 1)}) → {(3, 3), (6, −3), (−4, −1), (1, 6)}Prompt: Check the first coordinates in each set.
3. Is this relation a function? {(5, 7), (6, 2), (7, 8), (2, 8), (4, 5)} (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 = {(−3, 6), (4, 9), (6, 1), (0, −6)}. What is the domain of R? ({−6, −3, 0, 1, 4, 6, 9} / {−6, 1, 6, 9} / {−3, 0, 4, 6} / {−3, 0, 4}) → {−3, 0, 4, 6}Prompt: Domain: all the inputs (first numbers). Range: all the outputs (second numbers).
2. The function f = {(−2, 6), (6, −2), (0, −2), (5, 6), (4, 2), (−1, 2)}. 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 = {(3, 8), (2, 3), (−2, 7), (5, 3), (4, 7), (−4, 8)}. How many different values are in its range? → 3Prompt: The range is the set of outputs.
2. R = {(7, 5), (6, −6), (9, 9), (1, −1)}. What is the domain of R? ({1, 6, 7} / {−6, −1, 1, 5, 6, 7, 9} / {−6, −1, 5, 9} / {1, 6, 7, 9}) → {1, 6, 7, 9}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.