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

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