Russian Mathematics Education: Programs and Practices
manner, factor out common factors in numeric sums and products, and
so on. Two examples:
Example 1. Students are asked to find the value of the product
4
· 7 · 11 · 25 (Dorofeev, Sharygin et al., 2007a, p. 84).
They reason in the following manner: the product of 4 and 25
equals 100, and multiplying by 100 is easy, and therefore let us group
the factors in the following way:
4
· 7 · 11 · 25 = (4 · 25) · (7 · 11) = 100 · 77 = 7700.
Example 2. Students are asked to find the value of the fraction
1
3
−
1
5
2
3
−
1
2
(Dorofeev, Sharygin et al., 2007b, p. 11).
To find the value of this expression, the students can perform three
operations: find the value of the fraction’s numerator, find the value of
the fraction’s denominator, and divide the former by the latter. But they
can also employ a different approach: using the “basic property of frac-
tions” (the fact that multiplying the numerator and the denominator of
a fraction by the same number produces a fraction that is equal to the
original fraction), they can manipulate the given “multistory” fraction
and obtain the answer much more easily and quickly. The students’
reasoning is approximately as follows: let us multiply the numerator
and the denominator of the fraction by a “convenient” number to get
rid of the fractions in the numerator and the denominator. In the given
case, this number can be, for example, 30:
1
3
−
1
5
2
3
−
1
2
=
30
·
1
3
−
1
5
30
·
2
3
−
1
2
=
10
− 6
20
− 15
=
4
5
.
Of course, this solution is presented as an alternative to the first.
Although it is demonstrated to all students, the teacher emphasizes that
it makes sense to proceed in this way if the intermediate computations
can be performed mentally.
Performing transformations of this kind constitutes a good, sub-
stantive form of practice, which prepares the students for learning to
carry out transformations of literal expressions, which, as has already
been noted, are a topic of study at the subsequent stage (grades 7–9) —
as is solving equations by using transformations. At this stage, however,
March 9, 2011
15:2
9in x 6in
Russian Mathematics Education: Programs and Practices
b1073-ch04
On Algebra Education in Russian Schools
149
the aim of this activity is not so much the development of a skill as the
simple process of carrying out such transformations.
4.1.3
Algebra for students of ages 12–15 (grades 7–9)
In all textbooks for this stage, including those examined in this
chapter, the quantity of algebraic material is practically identical. It
is determined by the contents of the corresponding section of the
Standard, cited above.
Literal numeration. The presentation of algebraic material at this
stage most often begins with a section that can be labeled “Introduction
to Algebra.” Its content depends substantially on which textbook was
used at the previous stage and how much algebraic preparation students
received during that period. If the textbooks belonged to the series
by Makarychev et al., then they begin with systematization of the
knowledge acquired during the preceding stage — students again go
over the basic skills connected with combining like terms, removing
parentheses, and simplifying products; they are also introduced to such
concepts as identity and identity transformations of expressions. Here,
too, students again review material connected with solving equations,
are introduced to the concept of equivalent equations, and investigate
how many solutions an equation of the type ax + b = 0 has, depending
on the values of the coefficients a and b.
The textbooks by Dorofeev et al. begin by listing the properties of
arithmetic operations (in literal notation), which are already known
to the students, after which the students use numerical examples
to write down literal equalities that express certain computational
techniques, such as the technique of subtracting a sum from a number:
Do'stlaringiz bilan baham: |