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A Fourth Skill For Algebra
Direct and Indirect Use of Formulas, or Forwards and Backward Use of Equations
To learn more, visit Teaching-tutor Algebra
How-TOs
Every formula met in mathematics, accounting, science, technology etc may be
used directly and indirectly, that is forwards and backwards.
The simple message that the forward and backward use of formulas (direct
and indirect use) is part of high school mathematics and beyond
names a required skill and allows us to recognize, identify and thus emphasize
the most frequent pattern in high school mathematics and beyond.
This message needs to be given explicitly and early in secondary mathematics.
Otherwise the underlying skill become part of the hidden, or silent and unspoken,
agenda in mathematics courses.
Teachers: Consider combining the www.purplemath.com
a two page lesson on solving
literal equtions with the message above and the examples and exercises
indicated below. The page banner above was Forward and Backward use of
equations but it now reflects the purplemath lesson, Solving Literal
Equations.
First Site Example
Direct and Indirect Use of the Rectangle Area Computation Formula
Chapter 10
in Three
Skills for Algebra in discussing
Direct use of A =WL assumes W and L are given. Indirect use assumes A and one
of W and L is given, and leads to the calculation or formulas W = A/L or L =
A/W. The explanation of those formulas is a step towards algebraic
reasoning - the direct and indirect or forward and backward use of formulas.
More Examples: Formulas for perimeters and areas of
squares, circles, triangles, rectangles etc can be used forwards and
backwards. Finding the value of a proportionality constant k say in an
equation y = k x represents an indirect or backwards use of an equation,
a pre-requisite to further forward and backward use of the equation y = kx.
The calculation of parameters a and b in y = ax + b (or y = mx +b) represents
another backward use of a formula or equation. Quebec students in
secondary III have met the forward and backward use of the Pythogorean
equation c2=a2+b2 where c is the length of
the hypotenuse and the two numbers a and b are the lengths of the other two
sides (legs) of a right triangle.
To Do: : Post some details and exercises here
to further illustrate and emphasize the forward and backward use of common
formulas.
Going Further (More on Substitution)
The aforementioned Chapter
10 before the forward and backward use of a formula goes further in showing
how to describe a the calculation of a box V = H(WL) and show how to employ
substitution (a new concept for students) to go between this formula and V
= HA where A = WL. Details are given in the chapter. The
details may be easier to grasp if numerical examples are added to this
exposition.
Seeing how a box volume formula V = hA and V = h
(WL) can be transformed into each other illustrates and may introduce the
notion of equivalent expressions. The law applied here is A = WL is a
geometric law rather than an algebraic law (like the distributive law).
None, the idea that an expression represents a number or quantity and that
there may be more than one ways to compute the number or quantity is key to
the notion of equivalence. Students thus see how substitution in
formulas leads to new formulas, how arithmetic patterns may be used to
use formulas directly and indirectly, and how algebraic solutions may be more
general or powerful than arithmetic solutions.
Algebraic Exercises:
- Find a formula for the area of square in terms of its perimeter
(easy)
- Find a formula for the area of circle in terms of its perimeter
(easy)
- Find a formula for the perimeter of square in terms of its areas
(harder)
- Find a formula for the perimeter of circle in terms of its areas
(harder)
See www.purplemath.com
two page lesson on solving
literal equtions for hints or to learn more.
The exercises could be easier after reading the first sections of Chapter
15 and Chapter
14 in Three Skills for Algebra. The chapter 15 material may be
easier..
The first sections in Chapter 15, Solving
Linear Equations in online site Volume, 2. Three
Skills for Algebra, derives an algebraic formula for the solution of
equations of the form ax + b = c, and so emphasize the use of algebraic
shorthand reasoning to imply solutions for many problems of a given form at
once. All the foregoing emphasizes the power of algebra, or the shorthand way
of writing and reasoning with letters in place of numbers. That being said,
numerical experience is still required with formulas and their graphs,
otherwise the connection between numbers and algebra may too weak.
A Deeper Site Example
for now or later or never.
This Chapter
14 introduces the direct and indirect use of the
compound interest formula A = P(1+i)n.
Chapter
14 presents algebraic and arithmetic solutions that may be used to
check the calculator skills of students while developing the algebraic way of
writing and reasoning. In the compound interest formula A = P(1+i)n
three of the four amounts A, P and i and n are assumed known, and the problem
is calculate or find a formula for the missing fourth. The use of this formula
is indirect when the left hand side quantity A is given or known, and the task
is to find the value of the principal P, the interest rate i or the number of
compounding periods n. Add to chapter 14 coverage, numerical
confirmation that the algebraic solution works. The algebraic solutions
for the indirect use of formulas involve substitution and assumes the
pattern (AB)/B = A. Coverage of Chapter 14 is recommended as
part of the next topic: exponents and radicals.
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Three Skills
For
Algebra
Volume 2
Printed in Canada
ISBN 0-9697564-2-9
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Read slowly, this work may enrich your
skills & knowledge. Take the risk.
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Chapters and Appendices
Foreword 1. Introduction 2. Implication Rules [4] 3. Chains of Reason [3] 4. Induction Mathematical 4. Romeo and Juliet 6 Old Language 5 Knowledge Islands [2] 7 Arith Skill Check [4 X 2] Arith Webvideos 7. The Next Chapters 8 The Three Skills 8 VNR-Concise-Encyclopedia PS. What is a Variable [8] 9. Algebra Talk [7] 10 Two More Skills[5] 11 Why Shorthand 12 Shorthand Usage [10] 13 What's Next PS: The 4-th Skill For Algebra 14 Compound Interest [6] 15 Linear Equations [5] 16 Painless Proofs 17 Pythagoras PS I. Distributive Law PS II. Polynomials 18 Rules of Algebra [20] 19 Functions & Sets 20 Degrees & Radians 21 What's Next 22. Arith & Geometric Sums [2] 23 Summation Notation 24 Your Money [3] 25 Induction & Recursion [4] 26 What's Next 27 Pronouns in Logic 28 Occurrence Tables 29 Contrapositive 30 Truth Tables 31 Indirect Reason Pathways for Learning
Book Entrance
What is a Variable?
Introduction
Variation between Examples
Variation of Letters
A letter denotes a variable
Cases of Double Variation
Three Notions of a Variable
Constants, Parameters
& Variables
Talking about numbers
Dependent
or Independent
Variable, a Matter of Choice
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For
Senior
High School & Calculus Students
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Words to clearly
introduce algebra and variables
have been missing in course design. For people who cannot do
algebra,
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the missing words may
explain or ease their difficulties. Volume 2 ,Three
Skills for Algebra, in Chapters
8 to 14 & 18 etc, puts words before symbols to
providing the missing words in a way that enrich the
comprehension of all. Those words form the middle part of a algebra
(and logic) lessons aimed at helping or improving all
of high school mathematics and also calculus course
design & delivery.
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For Avid Readers in School & Out -
Online Books
1. Elements of
Reason. 1996
1A. Pattern
Based Reason 1995
1B. Math
Curriculum Notes 1996
2. Three
Skills for Algebra 1995
3.Why
Slopes & More.Math
1995
Tour their forewords.
Calculus Prep or Help: See Volumes 2 & 3,
and this bigger
Calculus
Guide. If your
calculus questions is not answered here, submit
it. Over time, that may complete the site development of
calculus.
For Parents: Speaking
Skills, Reading
& Writing,
Preparing for Science, ends,
values and methods for work and study, parent- friendly maths
skill development booklets for ages 4-14.
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Mostly
For High
School
Intro to Solving
Linear Equations
- a different paths for junior and even senior high
school students. Question for Tutors: When do
you use and when you skip the stick diagram method
here?
Fraction
Skills, thought-based development, Ages 10 to 14 may need a
tutor. Students who have to understand in order
to do may like the development in all or part.
For Senior
High School Mathematics & Calculus
5
wordy Logic
Chapters
4 curious Algebra
Chapters
Words before & besides symbols. A Key Algebra
forward & backwards Chapter
First Calculus
Preview (1st intro)
Four Calculus
Chapters
(2nd intro)
Intro to Complex
Numbers (long)
Intro to Mathematical
Induction (romantic & wordy at first)
Tutors & Instructors:
These lessons introduce skills differently Would you
recommend them?
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More Topics
1. Decimal
Arithmetic Reference!
2. Integers
- Intro to Signed No.s
3. Fractions
- fully explained.
4. Fractions
with Units
5. Number
Theory,
6. Solving
Linear Equations
7 Formulas
for- & backwards -
8. Proportionality,
Back- & For-wards.
9. Logic
Chapters:
10. Euclidean-Geometry
11. Slopes
& Equations of Straight Lines. (Take
I. See take II below)
12. Why
Study Slopes.
13. Maps,
Plans, Similarity & Trig,
(Take II included here)
14. Quadratics:
Starter lessons
15. Polynomials:
Starter lessons
16 Why
Factor Polynomials:
17 Functions
- Forwards & Backwards.
18. Exponents,
Radicals & logs.
19. Complex
Numbers before trig (new advance/ starter lesson)
20. DC
Electric
Circuits Etc
21. Real
Analysis
22. The
Olde Complex No, Trig
& Vector Section.
23. More
Calculus Stuff
- written after Volumes 2 and 3.
Level I Material: New Stuff
Time and Date Matters
Level I Arithmetic.
Money Matters
Measurement Matters
Matters of Chance (Risk Control)
Logic
Chapters
(leave what's not clear in Level I to Level II)
Using/Making Maps and Plans.
(A variant of
Maps,
Plans, Similarity & Trig, to
appear here).
For Instructors
-
Education
Essays
(opinions,
possibilities, references)
- Free
Advice and Directions for teaching primary & high school maths
will be given in online meeting place with voice &
whiteboard.
- Math & Logic How-TOs
1. Arithmetic
2. Algebra
3. More Algebra
4. Beginner Geometry
5. More Geometry
6. Calculus
7. Show Work or Logic
These may be too dense for students. Offering ideas to change
education makes this site different. Nothing
ventured, nothing gained. Site material is
mathematically correct, and where not, please report
errors. The two level program POMME in the site
entrance implies multiple paths for instruction. Supporting
those paths in turn implies a clear destination for
site development and perhaps a new name.
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