NUMBERS/NUMBER THEORY
- Division by 0
- Rational and Irrational Numbers
- Counting the Infinite: A Glimpse at Infinite Sets
- Is 0.999… really equal to 1?
- Prime Series 1: Introduction to Prime Numbers
- Prime Series 2: The Intuition Behind the Infinitude of Primes
- Prime Series 3: Proof of the Infinitude of Primes
- Making Sense of Exponential Growth
- Counting the Real Numbers
- Young Gauss and the Sum of the First n Positive Integers
- Dominoes and Mathematical Induction
- Pythagorean Triple 1: The Infinitude of Pythagorean Triples
- Pythagorean Triple 2: Generating Pythagorean Triples
- Large Numbers and One Million
- Light Year and the Mathematics of the Stars
- The Geometry of Commutativity
- The Distributive Property
- The Commutativity of Real Numbers
- Military Drills and the Closure Property of Real Numbers
- Finger Math 1: Finger Multiplication
- Finger Math 2: Why Finger Multiplication Works
- Understanding Fermat’s Last Theorem
- Irrational Numbers as Decimals
- Order of Operations: 360 or 354?
- The mysterious 495
- The mystery of 495 exlpained
- The Golden Ratio
- The Kaprekar constant 6714
- Operations on Integers – Addition
- Operations on Integers – Subtraction
- Operations on Integers – Discovering multiplication and division of integers using patterns
- Real Numbers: A summary
- Is 0 a natural number?
- Multiplication of Fractions
- Linking sum of counting numbers to triangle area
- Pi to 10 Trillion Digits
- Using Area to Prove the Arithmetic Mean-Geometric Mean Inequality
- Another Proof of the Sum of the First n Positive Integers
- Counting the Number of Squares on a Chess Board
- Prime or Not: Determining Primes Through Square Root
- Triangular Numbers and the Sum of the First n Positive Integers
- Introduction to Clock Arithmetic and Modular Systems
- Clock Arithmetic and Modular Systems Part 2
- Introduction to Number Bases
- Why Expressions with Negative Exponents Equal their Reciprocals
- Finding the General Formula for the kth Polygonal Number
- Why are Non-terminating, Repeating Decimals Rational
- Are all objects with irrational lengths measureable?
- Approximating Square Root of Numbers by Averaging
- How Big is Infinity?
- The Definition of Congruence in the Modular Systems
- The Clock Arithmetic and Modular Systems Series
- Guest Post: An Interesting Property of Prime Numbers
- Why The Addition Number Trick Works
- Properties of Addition and Multiplication of Real Numbers
- Are all fractions rational numbers?
Complex Numbers Series
- What is i? What are imaginary numbers?
- Complex Numbers and Their Properties
- Demystifying Complex Conjugates
- Introduction to the Complex Plane
The Divisibility Series
- Divisibility by 2
- Divisibility by 4
- Divisibility by 5 and 10
- Divisibility by 3
- Divisibility by 7 and its Proof
- Divisibility by 8
- Divisibility by 9
ALGEBRA
- Making Connection Between Distance and Absolute Value
- Letters, Variables and Algebraic Expressions
- Matchsticks, Linear Relations, and Multiple Representations
- Equation of a line: The derivation of y = mx + b
- Slope Concept 1 – Understanding the Basic Concepts of Slope
- Slope Concept 2 – Slope of the Graph of a Linear Function
- Slope Concept 3 – Slopes of Vertical and Horizontal Lines
- Arithmetic Sequences and Linear Functions
- Derivation of the Quadratic Formula
- Understanding the Meaning of Discriminant
- Geometric Sequences and Series
- Why do we reverse the inequality sign?
- Why is any number raised to 0 equals 1?
- Why is zero factorial equals 1?
- How to use the summation symbol
- Compound Interest and the Irrational Number e
- Functions 1: Introduction to the Concept of Functions
- Functions 2: Basic Concepts of Functions
- Vectors, Parallelograms and Commutativity
- Simon’s Favorite Factoring Trick
- Addition of Coordinates
- The Handshake Problem and Its Multiple Solutions
- The Multiplication Parabola
- Mathematical Equations and Their Properties
- The 12 days of Christmaths and the Triangular Numbers
- Why is the slope of a vertical line undefined?
- Deceptive and Misleading Mathematical Patterns
- Visualizing the Difference of Two Squares
- Why is negative times negative equals positive?
- Guest Post: Why Study Algebra
- The Polynomials that Generate Prime Numbers
GEOMETRY
- Chess and Axiomatic Systems
- Angle Sum of Polygons
- Why is the angle sum of the interior angles of a triangle equal to 180 degrees?
- Parallel Lines and Transversals
- The Exterior Angle Theorem
- Is there an SSA Congruence?
- Making Connections among Pythagorean Theorem, Distance Formula and Equation of a Circle.
- The Algebraic and Geometric Proof of Pythagorean Theorem
- Tessellation: The Mathematics of Tiling
- Is a square a rectangle?
- The Inscribed Angle Theorem
- Demystifying Triangle Inequality
- Constructing Segments with Irrational Lengths
- Similarity 1: Introduction to Similarity
- Similarity 2: Properties of Similar Triangles 1
- Similarity 3: Properties of Similar Triangles Part 2
- A Closer Look at the Midpoint Formula
- Eratosthenes and the Earth’s Circumference
- Platonic Solids: Why only five of them?
- Regular Tessellations: Why only three of them?
- The Seven Bridges of Konigsberg
- Discovering Properties of Parallelograms
- The Marvels of the Nine-Point Circle
- Introduction to Coordinate Geometry
- Undefined terms: What are they?
- Diagonals of a Parallelogram
- A US President’s Proof of the Pythagorean Theorem
- Which is the most pleasing rectangle?
- Understanding the Meaning of Correspondence
- Introduction to Geometric Construction
Area Tutorial Series
- Area Tutorial 1 - Introduction to the Concept of Area
- Area Tutorial 2 – Area of a Triangle
- Area Tutorial 3 – Area of a Parallelogram
- Area Tutorial 4 – Area of a Circle
- Area Tutorial 5 – Area of a Trapezoid
TRIGONOMETRY AND PRECALCULUS
- Demystifying Degree and Radian Measures
- An elementary proof of the cosine law
- Folding a Hyperbola
- The Complements Theorem
- Pi and the Circle
- Jeepneys and Step Functions
- The Proof of the Tangent Half-Angle Formula
- Understanding Decreasing and Increasing Functions
Curve Sketching (New!)
- Graph Sketching 1: 4 Easy Ways to Graph a Linear Function
- Curve Sketching 2: Graphing Quadratic Functions
- Curve Sketching 3: Understanding Vertical and Horizontal Asymptotes
- Curve Sketching 4: Identifying Oblique Asymptotes
CALCULUS
- An Intituive Introduction to Limits
- An extensive explanation about the
definition of limits
- Limit by
proof: Example 1
- Limit by
proof: Example 2
- Derivative Concept 1: The Algebraic and Geometric Meaning of Derivative
- Derivative Concept 2: Derivative in Real Life Context
- Derivative Concept 3: Derivative and the Maximum Area Problem
- Calculating the Area Under a Curve: An Intuitive Introduction
The Calculus Primer Series
STATISTICS, PROBABILITY AND COMBINATORICS
- Introduction to Permutations
- Introduction to Combinations
- Binomial Theorem Series 1: Milkshakes, Beads, and Pascal’s Triangle
- Binomial Theorem Series 2: The Binomial Expansion
- A Gentle Introduction to Probability
- The Unfinished Game Problem
- Using Mathematics to Win the Lottery
- Storytelling and Statistics at their finest
- Ben Goldacre and Bad Statistics
- Understanding the Multiplication Principle
- Probability Terminologies and Notations
- Wedding Guests and Circular Permutations
- Understanding Sample Space and Sample Points
Experimental and Theoretical Probability Series
PROOFS
- Proof Tutorial 1: Introduction to Mathematical Proofs
- Proof Tutorial 2: Proving the Irrationality of Square Root of 2 by Contradiction
- More examples of Proof by Contradiction
- Proof that log 2 is irrational
- Proof by Contradiction: Knights and Liars
- Another Proof of the Sum of the First n Positive Integers
- The Proof of the Tangent Half-Angle Formula
- A Simple Proof of the Arithmetic Mean Geometric Mean Inequality
- Using Similarity to Prove the Pythagorean Theorem
- Proof of the Sum of Square Numbers
- Mathematical Proofs Without Words: What are they?
- A Proof that the Vertex Angle Sum of a Pentagram is 180 degrees
- Proof without Words: Odds and Squares
- Understanding If Then Statements and Counterexamples
MATH LITE (Fun, Games, Puzzles, Trivia)
- Funny Math – 10 Steps you Need to Solve a Calculus Problem
- The Square Root of Three
- Why Mathematics Teachers Drink Part 1
- Why Mathematics Teachers Drink Part 2
- Men, Women, and Mathematics
- Amazing Number Patterns
- Simba sings math
- Math is …
- Nature by Numbers: Watch and fall in love with math
- Potato chips and mathematics
- Math Easter Egg
- Calculus Rhapsody
- Three
- Math Words in Filipino
- Calculating the volume of a pizza
- Math, Santa and Venn Diagrams
- Tangled and the Mathematics of Hairdressing
- The Beauty of Narcissistic Numbers
- Heart Graph for the Mathematically In Love
- Would you have given a different mark?
- Why Every Proof that 0.999… = 1 is Wrong
- Mathematics and Perspective
- Can you solve the hardest Sudoku puzzle yet?
- 11 Mathematical Proof Techniques Liberal Arts Majors Should Know
- Apple and the Golden Ratio?
- The Musical Beauty of Tau
- The Magic Circle Puzzle
- Teaching Math Like a Boss
- Who’s the Winner
- The Sound of Pi
- Grading Test Papers Like a Boss
- Watch Exceptional Fast-Paced Math Videos at Vi Hart
- How many squares are there?
- Pi In The Sky, Literally
- What if your paycheck…
- Matchsticks and Squares
- Origami and Its Surprising and Stunning Applications
- The Mathematics of Christmas Wrapping
- Taylor, Mathematics, and Perspective
- The Cycloid and the Pendulum Clock
MISCELLANEOUS Math Word Problem Solving Series Age Problems
Motion Problems
Vedic Mathematics (by Sanjay Gulati)
- Introduction to Vedic Mathematics
- Squaring Numbers in 5
- Multiplication with a series of 9s
- Nikhilam Method of Multiplication
- Nikhilam Method of Multiplication 2
- Squaring Numbers: Part 1
Paper Folding
- Getting the square root of any number on a number line
- Paper Folding: Extracting the cube root of a number
- Paper Folding: The proof of the cube root applet
- Origami and GeoGebra — a slightly different version
Set Theory
- Sets: A Gentle Introduction
- Subset: A set contained in a set
- Sets: Terminologies, Notations, and Operations
- Counting the Number of Subsets in a Set
- Are all infinities created equal?
General Information/Miscellany
- The Mystery Behind the Proof of 1 = 2
- The Search for Magic Squares
- The definition of Undefined
- Is mathematics and exact science?
- Steven Strogatz
- Making Mathematicians I
- How do mathematicians greet happy valentines?
- SOMEBODY up there pushed me
- Would you have made it into Harvard in 1869?
- All time Top Mathematics Posts
- A Hundred Years Down the Road
- The man who conned a mathematician
- 10 Ways to Think Like a Mathematician
- Applying Mathematics to Web Design
- Mathematics and the Love of God?
- 25 Signs You’re a Future Mathematician
- Who Owns the Zebra?
- Lottery Math — If you play, you should know your odds
- The Mathematics of Leap Years Explained
- The 10 Misfortunes of Evariste Galois
- Where is the Nobel Prize in Mathematics?
- Millenium Prize Problems: Problems Worth $1M Each
- 7 Extraordinary Mathematicians You Should Know About
- The Actual Fermat-Pascal Correspondence
MATH RESOURCES/FREEBIES
- More than 20,000 contest problems and solutions
- 8000+ Math, Physics, and Engineering applets
- Calculus 1 Video Lectures
- 8 Free Online Graphing Tools
- Mu Alpha Theta: 10,000+ Math Contest Problems with Solutions
- Wholemovement and The Art of Folding Circles
- The Prime Composite Dance
MATH TEACHING AND PEDAGOGY
- Math Exercise, Problem Solving, and Investigation
- The Inverted Classroom
- Conrad Wolfram: Teaching kids real math with computers
- When do mathematical definitions matter?
- Exploring Computational Thinking
- Math Curriculum Makeover
- What is Universal Design Learning
- Popularizing Lesson Study
- Using Paper Folding to Introduce the Notion of Proof
- 10 Tips in Studying School Mathematics
- Constructing Open -Ended Math Problems
- A Mathematician’s Lament
- 10 Reasons Why Mathematics Teachers Should Blog
- An Open Letter to New Teachers
- Common Errors in MDAS Operations
- PEMDAS and the Common Errors in the Order of Operations
- 4 Common Errors in Calculating Expressions with Exponents
- The Trigonometric Ratio Hexagon








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Why 0.999999999… = 1?
This equality usually surprises everybody. This is a short explanation:
Clearly
0.3333333333… = 1/3
Multiply both members by 3:
3*0.3333333333… = 0.99999999999… = 3*(1/3) = 1
Another way to go…
x = 0.999999999…
10x = 9.999999999…
Subtract the two and the infinite decimals cancel out
10x – x = 9x =9
x = 1
Hence 0.999999999… = 1
Right you are Karl. Thanks.
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sir saan po b pwede ma view ung mga sagot sa questionare ng math sa ALL-UP workers uniion CSC review..
maraming salamat po!
naipost ko na sa http://mathandmultimedia.com/2012/04/25/up-union-civil-service-review/