"Writing sets of natural numbers using set-builder and roster forms"

Writing Sets of Natural Numbers

Key Concepts

• Roster Form

  • A way to write a set by listing its elements within braces {}.
  • Example: The set containing the first three natural numbers can be written as {1, 2, 3}.

• Set-Builder Form

  • A compact way to specify a set by stating the properties that its members must satisfy.
  • Involves a variable (often x) and uses a vertical bar | meaning "such that."
  • Example: The set of all natural numbers greater than 2 can be expressed as {x | x is a natural number and x > 2}.

Roster Form Example

• Given Set: The set of all natural numbers greater than 6.
  • Roster Form: {7, 8, 9, 10, …}
  • Explanation: Start from 7 and include all natural numbers onward.

Set-Builder Form Example

• Given Set: The natural numbers between 16 and 18, inclusive.
  • Set-Builder Form: {y | y is a natural number and 16 ≤ y ≤ 18}
  • Explanation: y can take any natural number value from 16 to 18, including both endpoints.

Steps to Convert Between Forms

1. Identify the Set Elements: Determine the characteristics/intervals defining the elements.
2. Choose the Appropriate Variable: Decide an appropriate variable (e.g., x or y).
3. Write in Roster Form: List the first few elements of the set.
4. Transition to Set-Builder Form: Form an inequality or condition using the chosen variable.

Practice Problems

• Convert to Roster Form: Write the set of all natural numbers greater than 6.
• Convert to Set-Builder Form: Write the set of natural numbers between 16 and 18 in set-builder notation.