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# Mathematics and Logic - Skill and Concept Development

Online Volumes: 1 Elements of Reason || 2 Three Skills For Algebra || 3 Why Slopes Light Calculus Preview or Intro plus Hard Calculus Proofs, decimal-based.
More Lessons &Lesson Ideas: Arithmetic & No. Theory || Time & Date Matters || Algebra Starter Lessons || Geometry - maps, plans, diagrams, complex numbers, trig., & vectors || More Algebra || More Calculus || DC Electric Circuits || 1995-2011 Site Title: Appetizers and Lessons for Mathematics and Reason

Mathematics Concept & Skill Development Lecture Series: Webvideo consolidation of site lessons and lesson ideas in preparation. Price to be determined.

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#### Key Lessons for

##### For Arithmetic

Deciml Place Value - funny ways to read multidigit decimals forwards and backwards in groups of 3 or 6, US-CDN, UK-German and Metric SI style.

Decimals for Tutors - lean how to explain or justify operations. Long division of polynomials is easier for student who master long division with decimals.

Primes Factors - Efficient fraction skills and later studies of polynomials depend on this.

Fractions + Ratios - See how raising terms to obtain equivalent fractions leads to methods for addition, comparison, subtraction, multiplication and division of fractions.

Arithmetic with units - Skills of value in daily life and in the further study of rates, proportionality constants and computations in science & technology.

##### For Algebra

What is a Variable? - this entertaining oral & geometric view may be before and besides more formal definitions - is the view mathematically correct?

Formula Evaluation - Seeing and showing how to do and record steps or intermediate results of multistep methods allows the steps or results to be seen and checked as done or later; and will improve both marks and skill. The format here allows the domino effects of care and the domino effects of mistakes to be seen. It also emphasizes a proper use of the equal sign.

Solve Linear Eqns with & then without fractional operations on line segments - meet an visual introduction and learn how to present do and record steps in a way that demonstrate skill; learn how to check answers, set the stage for solving word problems by by learning how to solve systems of equations in essentially one unknown, set the stage for solving triangular and general systems of equations algebraically.

Function notation for Computation Rules - another way of looking at formulas. Does a computation rule, and any rule equivalent to it, define a function?

Axioms [some] as equivalent Computation Rule view - another way for understanding and explaining axioms.

Using Formulas Backwards - Most rules, formulas and relations may be used forwards and backwards. Talking about it should lead everyone to expect a backward use alone or plural, after mastery of forward use. Proportionality relations may be use backward first to find a proportionality constant before being used forwards and backwards to solve a problem.

www.whyslopes.com >> Volume 2 Three Skills For Algebra >> Chapter 8 Three Skills For Algebra Next: [Chapter 9 Talking about Numbers or Quantities.] Previous: [Solutions For Arithmetic Exercises.]   [1] [2] [3] [4] [5] [6] [7] [8] [9] [10][11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42]

# Chapter 8. Three Skills For Algebra

Volume 2, Three Skills for Algebra

Talking about three skills and illustrating them with examples may be enough to go from a mastery of arithmetic to a mastery of algebra. In learning to talk, write, argue and possibly do arithmetic, we have mastered harder skills. In elementary school, we mastered the first two skills: the ability to talk about numbers and quantities and the ability to describe calculations. The third skill depends on the first two. The three skills are as follows.

• First, we can talk about numbers and quantities without doing any arithmetic. For instance, numbers and quantities may be big, small, known, measured, never known, changing or unchanging, private, top-secret, confidential, embarrassing, or simply forgotten. A number, measurement or quantity may be known to you but not to me. We can speak about numbers and quantities in many ways. Talking about numbers and quantities is an ability we all have. It is a part of mathematics that does not require us to do arithmetic. There is more to mathematics than just doing arithmetic or being given a formula and numbers to use in it.

• Second, we can describe calculations which we want to do or avoid or have someone else do, without doing any arithmetic. The description gives a recipe or a formula for doing a calculation. The description can be done with words alone or with shorthand notation. This shorthand notation is worth a thousand words. The first service of mathematics to other subjects lies in the description of calculations that can be done or repeated as needed. There is more to mathematics than just doing arithmetic or being given a formula and numbers to use in it.

• Third, we can change the way numbers and quantities are computed (or measured). Rules or properties of arithmetic tell us when different calculations or measurements give the same result. These rules are described using shorthand notation. That gives a second role to the shorthand notation. In the computation of numbers and quantities, we may replace a calculation by another, when both give the same result. And in the description of calculations, we may replace a calculation by a shorthand symbol that represents its result, and vice-versa. These replacement ideas, illustrated below with examples, allows us to compute or describe different ways to calculate a single number or quantity.
Algebra or the manipulation of formulas is concerned with the shorthand description of different computations and with when one description can replace another. Description of one calculation can replace the description of another in any circumstance where the two calculations give the same result. Such replacements can be made one at a time, or one after another. There is more to mathematics than just doing arithmetic or being given a formula and numbers to use in it.

The description of calculations that might be done is a first service of mathematics to other subjects. The creation of new calculations by changing old ones is a second service to all subjects using arithmetic. Mathematics after arithmetic is based on the above three skills and the ability to read exactly rules, patterns and definitions. For the latter, see the previous chapters on logic.

### Notes

1. The first skill, our ability to talk about numbers and quantities, is widely known. We can say whether or not a number is known, forgotten, unknown, small, large, changing or varying, constant or unchanging, confidential and so on. Thus we can talk about and describe numbers and quantities. This can be done before the very visible, but sometimes misunderstood, symbols, letters and written shorthand of algebra, is introduced. Talking about numbers and quantities represents a easily-spoken element of algebraic thought apart from the algebraic way of writing and recording such thoughts.
2. A number or quantity which may change in the circumstances of interest to us is called a variable. The common idea that all variables have to be given by letters has mislead many. As just suggested, talking about variables, that is numbers or quantities which may change or vary, can be done without from any reference to letters and symbols. That is the notion of a variable can be clarified or explained before any linkage to algebraic shorthand or symbols used to write and record calculations and further parts of algebraic thought.
3. How to compute the area of a rectangle can be described with words alone or with a formula A = WL. In contrast, the compound interest formula A = P(1+i)n and even more so, the quadratic formula

$x = \frac{-b+\pm\sqrt{b^2-4ac}}{ 2a }$

describe calculations in an algebraic and symbolic way. It would be a horrible exercise to describe what these formulas mean, do and represent with words alone and no symbols.

See the essay What is a Variable. It will show you how to talk about variables and constants before and besides symbols. That represents the first skill in action.

Chapter 14 here on the compound interest formula introduces the forward and backward use of formulas. All the rules and patterns met in mathematics, science and logic will be used forwards and backwards. You may think of that as unifying theme. Talking about it recognizes it and points to its appearance, again and again in mathematics, science and logic. Using formula backwards deliberately is a sign of intelligence.

The following chapters will talk about the above three skills, including the forward and backward use of formulas. I am not sure whether to classify the latter as part of the third skill, or as a fourth skill. You decide.

Talking about the three or four skills above, and talking about finding counts and sums by forming and adding subcounts and subsums, and talking about finding products by forming and multiplying subproducts expands the role of words in both arithmetic and algebra. Earlier is better than later in mathematics skill development.

www.whyslopes.com >> Volume 2 Three Skills For Algebra >> Chapter 8 Three Skills For Algebra Next: [Chapter 9 Talking about Numbers or Quantities.] Previous: [Solutions For Arithmetic Exercises.]   [1] [2] [3] [4] [5] [6] [7] [8] [9] [10][11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42]

Road Safety Messages for All: When walking on a road, when is it safer to be on the side allowing one to see oncoming traffic?

For students of reason in society, science and technology: Pattern Based Reason describes origins, benefits and limits of rule- and pattern-based thought and actions. Not all is certain. We may strive for objectivity, but not reach it. Postscripts offer a story-telling view of learning: [ A ] [ B ] [ C ] [ D ] to suggest how we share theories and practices.

##### For Logic

These online chapters may amuse while leading to greater precision and comprehension in reading and writing at home, in school, at work and in mathematics.

1 versus 2-way implication rules - A different starting point - Writing or introducting the 1-way implication rule IF B THEN A as A IF B may emphasize the difference between it or the latter, and the 2-way implication A IF and ONLY IF B.

Deductive Chains of Reason - See which implications can and cannot be used together to arrive at more implications or conclusions,

Mathematical Induction - a light romantic view that becomes serious.

Responsibility Arguments - his, hers or no one's

Islands and Divisions of Knowledge - a model for many arts and disciplines including mathematics course design. Site Theme: Different entry points may be easier or harder for knowledge mastery.

##### For Geometry

Maps + Plans Use - Measurement use maps, plans and diagrams drawn to scale.

Euclidean Geometry - See how chains of reason appears in and besides geometric constructions.

Coordinates - Use them not only for locating points in the plane or space.

Complex Numbers - Learn how rectangular and polar coordinates may be used for adding, multiplying and reflecting points in the plane, in a manner known since the 1840s for representing and demystifying "imaginary" numbers, and in a manner that provides a quicker, mathematically correct, path for defining "circular" trigonometric functions for all angles, not just acute ones, and easily obtaining their properties. Students of vectors in the plane may appreciate the complex number development of trig-formulas for dot- and cross-products. Lines-Slopes [I] - Take I & take II respectively assumes no knowledge and some knowledge of the tangent function in trigonometry.

What is Similarity - another view of using maps, plans and diagrams drawn to scale in the plane and space. May buildings in space are similar by design.

##### For Calculus

Why study slopes - this fall 1983 calculus appetizer shone in many classes at the start of calculus. It could also be given after the intro of slopes to introduce function maxima and minima at the ends of closed intervals.

Why factor polynomials - this 1995-96 lesson introduces calculus skills and concepts. It may also may be given to introduce further function maxima and minima both inside and at the ends of closed intervals.

Check Arith. Skills - too many calculus and precalculus students do not have strong arithmetic and computation skills. The exercises here check them while numerically hinting at equivalent computation rules.