Mathematics
Advanced
40 mins
Teacher/Student led
+65 XP
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Rules for Patterns Using Words and Tables

Learn to build term-number and value tables for growing patterns, write rules in words, and use them to leap straight to any term without listing every step.

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    1 - Getting Started ~4 mins

    Look at this pattern of tiles growing step by step: 3 tiles, then 5, then 7. It keeps growing the same way each time. We call which step we are on the term-number — so the 1st pattern is term-number 1, the 2nd is term-number 2, and so on — and we call how many tiles are in it the value. Here is the big question: how many tiles would be in term-number 10? And could you work it out without drawing all ten patterns?

    2 - Watch and Notice ~9 mins

    Example 1: term-numbers 1, 2, 3 into the machine

    Watch as we feed the term-numbers 1, 2 and 3 through the machine. Out come the values 3, 5 and 7. Look at how the values change: 3, then 5, then 7 — they go up by 2 each time. That jump of 2 is exactly what we multiply the term-number by, so the rule starts with × 2. But term-number 1 times 2 is only 2, and our first value is 3, so we need a + 1 to land on it. The rule is: take the term-number, times it by 2, then add 1.

    Example 2: the times-three rule

    Now a different machine. Feeding in 1, 2, 3 gives 3, 6, 9. These values go up by 3 each time, so we multiply the term-number by 3. Check the first value: term-number 1 times 3 is 3, which matches exactly, so we need no adding or taking away this time. The rule is simply the term-number times 3.

    Example 3: the times-four-take-one rule

    This machine gives 3, 7, 11 for 1, 2, 3. These values jump up by 4 each time, so we multiply the term-number by 4. But term-number 1 times 4 is 4, and our first value is only 3, so this time we take away 1 to land on it. The rule is the term-number times 4, then take away 1.

    3 - Try It Together ~7 mins

    Today we work through this together: we have a growing pattern that starts 3, 5, 7. Let's feed the next term-numbers through the machine, read off the values, and fill the table on the board. Before each one, see if you can predict the value first. Then we'll say the rule out loud: term-number times 2, plus 1.

    Build the term-number and value table

    4 - Build the Table in Your Copy ~3 mins

    COPYBOOK MOMENT

    In your maths copy, draw a two-row table. Label the top row 'term-number' and the bottom row 'value'. Fill in terms 1 to 5 for our pattern (3, 5, 7, then keep it going). Underneath the table, write the rule as a full sentence: 'The value is the term-number times 2, plus 1.'

    5 - Class Challenge ~8 mins

    Today's challenge is a hidden-rule investigation. We have a matchstick-square pattern, and the machine knows the rule but won't tell us. Let's send a few numbers of squares through, watch the matchsticks come out, build the table together, and work out the rule for ourselves. Once we have it, we'll leap all the way to the 50th pattern without counting up.

    Find the matchstick rule

    Pupil practice
    Module 10 · Algebra: Patterns, Expressions and Equations Mixed
    Lesson 105 · Rules for Patterns Using Words and Tables
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