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Cheatsheet: Piecewise Functions

1. Definition and Notation

1.1 Basic Definition

Term Definition
Piecewise Function A function defined by different expressions on different intervals of the domain
Domain Set of all input values (x-values) for which the function is defined
Range Set of all output values (y-values) produced by the function

1.2 Standard Notation

General form:

Notation Meaning
f(x) = { expression₁, if condition₁
         expression₂, if condition₂
         expression₃, if condition₃ }
Each piece applies only when its condition is true; conditions must cover entire domain without overlap

2. Writing Piecewise Functions

2.1 Domain Intervals

Interval Type Notation and Meaning
x <> All values less than a (open on right)
x ≤ a All values less than or equal to a (closed on right)
x > a All values greater than a (open on left)
x ≥ a All values greater than or equal to a (closed on left)
a < x=""><> All values between a and b (open interval)
a ≤ x ≤ b All values between a and b including endpoints (closed interval)
a ≤ x <> All values between a and b, including a but not b

2.2 Common Forms

  • Linear pieces: f(x) = mx + b on specific intervals
  • Constant pieces: f(x) = c (horizontal lines)
  • Quadratic pieces: f(x) = ax² + bx + c on specific intervals
  • Combinations of different function types

3. Evaluating Piecewise Functions

3.1 Step-by-Step Process

  1. Identify the input value (x-value)
  2. Determine which condition the input satisfies
  3. Use the corresponding expression for that piece
  4. Substitute the input value into the expression
  5. Simplify to find the output

3.2 Key Points

  • Each input corresponds to exactly one piece of the function
  • Check inequality symbols carefully (< vs="">
  • Endpoint values belong to the piece with ≤ or ≥
  • If evaluating at a boundary, determine which piece includes that x-value

4. Graphing Piecewise Functions

4.1 Graphing Steps

  1. Graph each piece separately on its specified interval
  2. Check endpoints: use closed dot (•) for included values (≤ or ≥)
  3. Use open dot (○) for excluded values (< or="">)
  4. Ensure each x-value has exactly one y-value on the graph
  5. Label important points (endpoints, intercepts)

4.2 Endpoint Notation

Symbol Graph Notation
≤ or ≥ Closed dot (•) - point is included
< or=""> Open dot (○) - point is not included

4.3 Graph Characteristics

  • Continuous function: no breaks or jumps in the graph
  • Discontinuous function: has breaks or jumps where pieces don't connect
  • Jump discontinuity: occurs when left and right pieces don't meet at a boundary
  • Vertical line test: still applies (each x has only one y)

5. Special Piecewise Functions

5.1 Absolute Value Function

Function Piecewise Form
f(x) = |x| f(x) = { x, if x ≥ 0
         -x, if x < 0="">
f(x) = |x - h| f(x) = { x - h, if x ≥ h
         -(x - h), if x < h="">

5.2 Step Functions

Type Description
Greatest Integer (Floor) f(x) = ⌊x⌋ rounds down to nearest integer; creates horizontal steps
Constant Pieces Horizontal line segments on different intervals; graph looks like steps

5.3 Real-World Applications

  • Tax brackets: different rates for different income ranges
  • Shipping costs: rates change based on weight ranges
  • Parking fees: rates change based on time intervals
  • Utility billing: tiered pricing structures

6. Domain and Range

6.1 Finding Domain

  • Combine all intervals from the conditions
  • Check if conditions cover all real numbers or specific intervals
  • Express using interval notation or inequality notation

6.2 Finding Range

  1. Evaluate or graph each piece on its interval
  2. Determine y-values produced by each piece
  3. Consider endpoints (included or excluded)
  4. Combine all possible y-values
  5. Express using interval notation or set notation

7. Continuity

7.1 Testing Continuity at a Point x = a

Condition Requirement
Left-hand limit Evaluate piece valid for x < a="" as="" x="" approaches="">
Right-hand limit Evaluate piece valid for x > a as x approaches a
Function value f(a) must be defined
Continuity Function is continuous at x = a if left limit = right limit = f(a)

7.2 Types of Discontinuity

  • Jump discontinuity: left and right limits exist but are not equal
  • Point discontinuity: limits equal but f(a) undefined or different
  • Check all boundary points where pieces meet

8. Solving Equations with Piecewise Functions

8.1 Solving f(x) = k

  1. Set each piece equal to k separately
  2. Solve each equation algebraically
  3. Check if solution falls within the interval for that piece
  4. Reject solutions outside their interval
  5. Combine all valid solutions

8.2 Example Process

For f(x) = { 2x + 1, if x < 3;="" x²="" -="" 5,="" if="" x="" ≥="" 3="" },="" solve="" f(x)="">

  • Piece 1: 2x + 1 = 7 → x = 3, but 3 is not < 3,="" so="">
  • Piece 2: x² - 5 = 7 → x² = 12 → x = ±√12, check x ≥ 3, keep x = √12 only
  • Solution: x = √12 or x = 2√3

9. Common Mistakes to Avoid

  • Using wrong piece when evaluating at boundary points
  • Forgetting to check if algebraic solution is in the correct interval
  • Confusing open and closed dots on graphs
  • Not covering entire domain (leaving gaps in conditions)
  • Overlapping conditions (multiple pieces for same x-value)
  • Misreading inequality symbols
  • Not simplifying expressions after substitution

10. Key Formulas and Relationships

10.1 Important Reminders

Concept Formula or Rule
Function definition Each x-value maps to exactly one y-value
Absolute value |a| = { a, if a ≥ 0; -a, if a < 0="">
Distance from h |x - h| measures distance from x to h on number line
Slope m = (y₂ - y₁)/(x₂ - x₁) for linear pieces
The document Cheatsheet: Piecewise Functions is a part of the Grade 10 Course Integrated Math 2.
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