The Results
Chan is 24 years 2 months old when he was interviewed. Currently, he is pursuing a 4-year Bachelor of Science with Education (B.Sc.Ed.) program at a local university. He majored and minored in mathematics and chemistry respectively. At the time of data collection, Chan was in his first semester of his third year studies. He attained 3.55 in the Cumulative Grade Point Average (CGPA) for his first two years of studies at the local university. He does not have any teaching experience prior to this interview.
The results showed that Chan had adequate procedural knowledge of calculating the perimeter of a composite figure, namely rectangle and parallelogram/triangle. He understood the properties of a rectangle or a parallelogram, such as the opposite sides of a rectangle or a parallelogram were of equal length. Thus, he succeeded in calculating the perimeter of the composite figure. His understanding of the properties of a rectangle or a parallelogram had also enabled him to develop the formula for calculating the perimeter of a rectangle and a parallelogram. The following excerpt shows his response in developing the formula for calculating the perimeter of a rectangle (Chan/CI/L1351-1358):
Excerpt 1
R: How did you get the formula?
S: …because rectangle, its opposite sides are same length. So, we can know the length of one side, we multiply it by two. The width also the same, so we multiply it by two. So, add these two, we get this formula ah.
Chan also had adequate procedural knowledge of calculating the area of a rectangle. He identified the formula for the area of rectangle PQTU as 'UP × PQ' (length × width) and got the answer correctly as 300 cm2. Chan knew that the formula for the area of parallelogram was 'base × height' but he had mistakenly used QR (slanted side) as the base and got the wrong answer as 136 cm2. Therefore, he got the wrong answer when he summed up the area of the composite figure in Task 12. Nevertheless, Chan had successfully applied the Pythagoras' Theorem to find the length of TR where TR = 8 cm. He 838
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sketched a right-angled triangle with the length of a and b, hypotenuse c, and then explained that the relationship c2 = a2 + b2 is the Pythagoras' Theorem.
Though Chan knew the formula for calculating the area of a rectangle and a parallelogram, he did not know how to develop these formulas. It showed that Chan had inadequate conceptual knowledge that underlied his understanding of these formulas. Excerpt 2 depicts his response in developing the formula for calculating the area of a rectangle (Chan/CI/L1394-1396, 1400-1402):
Excerpt 2
R: How would you develop or derive the formula for calculating the area of a rectangle?
S: …(quiet) ah never think ah.
R: If your student asks you, teacher, how to develop or derive this formula, how do you explain?
S: …(quiet) forget already ah.
However, Chan was able to explain the meaning of the base and the height in the area formula of a parallelogram. He explained that the height of a parallelogram was the perpendicular distance to the base.
Chan also knew that the formula for calculating the area of a triangle was '21 × base × height'. When he was asked to explain why was there 'a half' in the formula, Chan explained that a triangle is the same as 'a half' parallelogram. However, he lacked of confident to develop this formula. Excerpt 3 demonstrates his response in developing the formula for ca