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Indices inquiry

The indices prompt is suitable for 11- and 12-year-old children, although it can be adapted for older students.
    
Th
e inquiry starts with students trying to understand the diag
ram. It is better to delay any discussion about the meaning of the exponent until students have had the opportunity to raise questions about the diagram. In this way, the teacher can evaluate the existing level of knowledge in the class and consider the detail and duration of an explanation (if one is required). Moreover, the types of questions and comments will allow the teacher to decide whether any students can be asked to give that explanation.
   
Typical questions and statements that arise during the orientation phase are:
  • Why are numbers linked by lines?
  • Do the lines carry on in the same pattern?
  • What does the 'little 2' mean?
  • Why are there no lines going to 25 and 100?
  • Why are there four lines? Could there be more?
  • If the last digit (in the units column) is the same, the numbers are connected.
  • What happens if you extend the pattern 'downwards' into negative numbers?
  • Can you extend the pattern 'upwards'?
As the inquiry gets under way, the teacher should dispel any thoughts that 152 means 15 x 2 and not 15 x 15, thereby ensuring that the exponent is applied correctly. The main focus at this early stage, however, should be on explaining why some squares can be linked by the lines. Why, for example, do the squares of numbers ending in four and six always have six in the units column? By extending the pattern 'upwards', students find links for 5 and 10; extending the pattern 'downwards' has required students to multiply two negative numbers.
  
The prompt can be changed in the following ways:

  • Use a different exponent, such as 14, 24, 34, and so on. Students should decide if this activity is better arranged in separate groups or as a whole class. They can then explain the links between the unit digits.
  • Keep the base number the same and change the exponent, such as 71, 72, 73, and so on. Again, students can decide on the nature of a collaborative activity, before explaining the links between the unit digits.
  • Link numbers in other ways, such as link two numbers to their product (possibly guided by the teacher). So, for example, 22 x 52 = 102. Can the student prove that a2 x b2 = c2 if a x b = c? With the base number held constant, this could lead to an appreciation of the laws of indices. For example, if the base number is 3, 9 x 27 is linked to 243, which can be recorded as 32 x 33 = 35.
  • Use negative exponents (such as -2 instead of 2), which can lead to an independent inquiry for individual younger students or, perhaps, a jointly constructed understanding for older classes. 
The inquiry ends with students presenting their mathematical findings and evaluating their decisions on the course of the inquiry.

The indices prompt appeared in an article by Magdalene Lampert under the intriguing title of When the Problem is Not the Question and the Solution is Not the Answer published in the American Educational Research Journal in 1990. The article describes and analyses the discussions that occurred in one classroom about the prompt.

Resources
Prompt sheet (horizontal number line)
Promethean flipchart    download
Smartboard notebook   download

 
A contradiction encountered by extending patterns 
Professor Raffaella Borasi, in her book Learning Mathematics Through Inquiry (1992), introduces the students she is working with to the two patterns in the illustration. She writes: "If the heuristic of extending a pattern is applied when we try to evaluate 00, a potential contradiction follows, since two alternative patterns seem both possible and reasonable and yet each suggests a different value for the result." For Borasi, this is a fruitful contradiction because she is running a series of inquiries with two students into what constitutes a mathematical definition.
  
The patterns can form the basis of an interesting starter discussion with older students in secondary school. However, the discussion can become a bit messy with students taking sides on the basis of what 'feels right' to them. So, typically, they argue 00 must equal zero because 'there's nothing there' or 00 is one because the law of indices would not work if it was anything else. While there might be merit to both arguments, this is an opportunity for the inquiry teacher to remind students of the wider mathematical culture in which 00 is normally defined as one (although I note that Borasi supports the case for it remaining undefined).
  
One of the most novel responses I have had to these patterns was when a student suggested using a spreadsheet to see what xx equalled as x approached zero. The answer is one, although the spreadsheet, we decided, does not amount to a proof. When students graphed values (to two decimal places) between zero and one, they noticed that values for xx start to rise between 0.36 and 0.37. More broadly, the activity reminds students that they cannot extend patterns unquestioningly.
Questions and observations
These are the responses of Caitriona Martin's year 8 class to the indices prompt. Caitriona reports that the students noticed that the connected number differences go up in a sequence, which is a novel way of approaching the prompt. The observation that the squares of 5 and 10 have no lines attached to them can lead into a discussion about possible digits in the units column when you square numbers.


Caitriona is second-in-charge of maths at St Andrew's Catholic School, Leatherhead (UK). You can follow her on twitter @MrsMartinMaths.
   
A different representation  
The indices prompt was changed to this horizontal presentation to fit in conceptually with an exploration of the number line being carried out by year 7 mixed attainment classes at Longhill High School, Brighton (UK). The students had studied how to represent decimals and fractions on the number line and convert between them. Their learning then developed onto different types of numbers. 
  
The indices prompt was the students' first experience of inquiry learning in Year 7. The first lesson focussed on asking questions and making observations (above). Students went on in the second lesson to explore the patterns they had noticed. They represented the gap between the square numbers (consecutive odd numbers) by drawing squares in the first quadrant of an x-y graph starting from (0, 0). Alternatively students chose to answer the questions below about their observations at the start of the inquiry.
  

The questions and observations of a group of three students.