• Quick retrieval from earlier learning (Rational functions and asymptotes; Find limits of rational functions as x → ∞). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. Find the horizontal asymptote of f(x) = (4x − 5)/(3x − 18). Give the y-value (fractions allowed). → 4/3 (1 1/3)Prompt: For large x, compare the leading terms of top and bottom.
2. Find the limit as x → ∞ of (5x² − x + 3)/(x² − 2x − 1). Give a fraction if needed. → 5Prompt: For huge x, only the highest powers matter.
3. What happens to (6x + 1)/(3x² − 3) as x → ∞? (0 / 2 / No finite limit (it grows without bound)) → 0Prompt: Compare the degree of the top with the degree of the bottom.

• Show a "think of a number" puzzle and ask the class to work out the starting number.
• Share the objective: Find vertical and horizontal asymptotes. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: f(x) = (4x − 9)/(x − 1). Find the vertical asymptote x = ?
• Step 1: x = 1
• Answer: 1
• 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. f(x) = (−2x + 9)/(x + 3). Find the horizontal asymptote y = ? → -2Prompt: For large x, f(x) behaves like the ratio of the x terms.
2. What are the vertical asymptotes of f(x) = (4x² + 1)/(3x² − 12)? (There are none / x = 2 and x = −2 / y = 4/3 / x = 4 and x = −4) → x = 2 and x = −2Prompt: Set the denominator equal to zero.

• 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. f(x) = (x − 3)/(x − 6). Find the vertical asymptote x = ? → 6Prompt: A vertical asymptote is where the denominator is zero (and the top isn't).
2. What are the vertical asymptotes of f(x) = (5x² + 1)/(x² − 25)? (x = 5 / x = 25 and x = −25 / There are none / x = 5 and x = −5) → x = 5 and x = −5Prompt: Set the denominator equal to zero.

Free online practice with hints and printable worksheets for this skill: eurekami.com/math/grade-12.