x
The Language of the Unknown
Variables, Expressions, Equations & Algebraic Structure
The Human Problem
Arithmetic asks: 7 + 5 = 12. Everything is known. Algebra asks: What if one of the quantities is hidden? Suppose x + 5 = 12. Now x represents an unknown quantity. Arithmetic calculates particular answers. Algebra discovers relationships that work for whole families of numbers.
KNOWN QUANTITY →
UNKNOWN QUANTITY →
SYMBOL →
EXPRESSION →
EQUATION →
RULE →
GENERALIZATION
The 46 Algebraic Cells
From Variables to Quadratic Modelling
CELL 01
The Unknown
+ 3 = 8
- Known vs Unknown quantity
- The concept of a variable
- Symbol as a container
CELL 02
Variables
x
y
n
- Symbol whose value varies
- Representing an unknown
- Representing a changing quantity
CELL 03
Constants
3x+7
- Fixed numerical value
- Distinction from variables
- Constant terms in expressions
CELL 04
Algebraic Terms
4x + 3y - 7
- Meaningful pieces of expressions
- Separated by + or -
- Variable & Constant parts
CELL 05
Coefficients
7x
- Numerical factor of a term
- Implied coefficient of 1 or -1
- Scaling the variable
CELL 06
Like & Unlike Terms
3x and 5x (Like)
3x and 3y (Unlike)
- Same variable part
- Condition for combining
- Structural identity
CELL 07
Algebraic Expressions
2a - 7b + 4
- Combination of terms
- No equality sign
- Reading & writing expressions
CELL 08
Words → Algebra
"Three times a number"
↓
3x
- Language to math structure
- "Increased by", "Less than"
- Modelling reality
CELL 09
Substitution
x = 4
3x + 5 = 17
- Evaluating expressions
- Replacing variables with values
- Multiple variables
CELL 10
Simplification
3x + 5x
→
8x
- Combining like terms
- Reducing complexity
- Foundation for solving
CELL 11
Distributive Law
a(b + c)
↓
ab + ac
- Expanding brackets
- a(b+c) = ab + ac
- Bridge to factorization
CELL 12
Algebraic Identities
(a+b)²
≡
a² + 2ab + b²
- True for all values
- Identity vs Equation
- Common expansion patterns
CELL 13
Equations
3x+5 = 17
- Statement of equality
- Left-hand side (LHS) & RHS
- Finding the solution
CELL 14
Balance Principle
LHS
RHS
- Equation as a scale
- Equivalent operations on both sides
- Maintaining equality
CELL 15
One-Step Equations
x + 7 = 12
- 7
x = 5
- Single inverse operation
- + ↔ - and × ↔ ÷
- Isolating the variable
CELL 16
Multi-Step Equations
3x + 5 = 20
3x = 15
x = 5
- Sequential inverse operations
- Simplifying before solving
- Strategic isolation
CELL 17
Equations with Brackets
3(x+2) → 3x+6
- Applying distributive law first
- Expansion then isolation
- Managing complexity
CELL 18
Variables on Both Sides
5x + 2 = 2x + 14
- Collecting variables to one side
- Symbolic balancing system
- General linear equations
CELL 19
Fractional & Decimal Eq.
x3
+ 2 = 7
- Clearing denominators
- Handling decimal coefficients
- Arithmetic → Algebra bridge
CELL 20
Formulae
A = lw
↱
l = A/w
- Algebraic relationships
- Solving for a different variable
- Applications in science
CELL 21
Linear Inequalities
- Comparisons (>, <, ≥, ≤)
- Solution sets
- Number-line representation
CELL 22
The Sign Reversal Rule
x > 3
× (-1)
-x > -3
- Multiplying/dividing by negative
- Inequality direction flips
- Crucial conceptual trap
CELL 23
Simultaneous Equations
x + y = 10
x - y = 2
x=6, y=4
- Two variables, two equations
- Substitution method
- Elimination method
CELL 24
Two Variables
x + y = 5 → (2,3), (1,4)...
- ax + by + c = 0
- Infinite coordinate pairs
- Set of points
CELL 25
Linear Graphs
- Equation becomes geometry
- Plotting points on a line
- Slope and intercept preview
CELL 26
Polynomials
2x³ - 5x + 7
- Variables with integer powers
- Numerical coefficients
- Building blocks of algebra
CELL 27
Degree of a Polynomial
3x4 + 2x²
- Highest power of variable
- Leading coefficient
- Polynomial classification
CELL 28
Types of Polynomials
Linearx + 5
Quadraticx² + x
Cubicx³
- By terms (Monomial, Binomial)
- By degree (Linear, Quadratic...)
- Standard form
CELL 29
Polynomial Operations
(3x² + 2x) + (x² - 5x)
4x² - 3x
- Addition & Subtraction
- Combining like terms
- Structural rules applied
CELL 30
Polynomial Multiplication
x²
3x
2x
6
- Distributing terms e.g., (x+2)(x+3)
- Expansion into structure
- Bridge to factorization
CELL 31
Polynomial Identities
(a+b)(a-b) = a²-b²
- Standard expansion formulas
- Derived, not just memorized
- Higher identities (cubes)
CELL 32
Factorization
x² + 5x + 6
→
(x+2)(x+3)
- Reverse multiplication
- Common factor, grouping
- Splitting the middle term
- Revealing algebraic structure
CELL 33
Algebraic Fractions
x + 2
x - 3
- Expressions as fractions
- Simplification & Cancellation
- Restrictions (denominator ≠ 0)
CELL 34
Zeroes / Roots
- Values making p(x) = 0
- Connecting factors to roots
- Preparation for quadratics
CELL 35
Factor Theorem Preview
p(a) = 0
- If p(a)=0, (x-a) is a factor
- Remainder theorem basics
- Advanced school algebra bridge
CELL 36
Quadratic Equations
ax2 + bx + c = 0
- General form (a ≠ 0)
- Equations with squared terms
- Multiple solutions
CELL 37
Solving by Factorization
x² + 5x + 6 = 0
Sum=5, Prod=6
- Finding satisfying numbers
- Setting factors to zero
- (x-a)(x-b) = 0 principle
CELL 38
Quadratic Formula
x =
-b ± √(b² - 4ac)
2a
- Universal solution method
- Derived from completing the square
- Calculating complex roots
CELL 39
Discriminant
D = b² - 4ac
D>0D=0D<0
- Nature of roots (2, 1, or 0 real)
- D < 0 means no real roots
- Gateway to Complex Numbers
CELL 40
Completing the Square
- Foundational technique
- Connecting to vertex form
- Geometry of parabolas
CELL 41
Vieta's Relations
α+β = -b/a
αβ = c/a
- Sum and product of roots
- Relationship to coefficients
- Higher algebra bridge
CELL 42
Quadratic Graphs
- Parabola shape
- Vertex & Axis of symmetry
- Roots as x-intercepts
CELL 43
Algebraic Modelling
Area = x(x+5)
Solve for x
- Reality → Variables → Equations
- Age, Money, Distance problems
- Interpreting mathematical results
CELL 44
Checking Solutions
3(5)+2 = 17
- Verifying obtained answers
- Substituting back to original
- Mathematical rigour
CELL 45
Extraneous Solutions
x = -2 ✗
- Apparent solutions that fail
- Violating original restrictions
- Advanced equation preview
CELL 46
The Algebraic Hierarchy
- Number → Variable → Term
- Expression → Equation
- Polynomial → Root → Function
Exit Portal
We have named the unknown. We have built expressions, balanced equations, and factored polynomials. But what happens when we need to study collections of objects, logic, and truth itself?