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Describe a Number Relationship with Letters

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Expressions using Letter-Numbers · Letters representing numbers · 3:10

You'll learn: Translate a number relationship described in words into an expression with letters.

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Describe a Number Relationship with Letters

3:10

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Describe a Number Relationship with Letters

You'll learn: Translate a number relationship described in words into an expression with letters.

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Same topic

Letters representing numbers

1

How Can a Letter Stand for a Changing or Unknown Number?
3:04
How Can a Letter Stand for a Changing or Unknown Number?
You'll learn: A letter can stand for a quantity that changes or for one we don't know yet.

Next topic

Formulas from quantities

3

Write a Formula for a Total Cost
3:09
Write a Formula for a Total Cost
You'll learn: Write a formula for total cost as price times quantity.
Express an Age Relationship with a Letter
3:04
Express an Age Relationship with a Letter
You'll learn: Write one person's age in terms of another's using a letter.
Write Perimeter Formulas for Regular Shapes
3:09
Write Perimeter Formulas for Regular Shapes
You'll learn: The perimeter of a regular shape is the number of sides times the side length.

Next topic

Calendar and number-grid relationships

2

Write Relative Values in a Calendar or Number Grid
3:03
Write Relative Values in a Calendar or Number Grid
You'll learn: Write every cell of a calendar or grid block relative to one cell, using row and column rules.
Why Do the Diagonal Sums Match in a Number Grid?
3:17
Why Do the Diagonal Sums Match in a Number Grid?
You'll learn: Using a letter for one corner shows both diagonal sums are always equal.

Next topic

Evaluating algebraic expressions

2

Substitute a Number Without Changing the Expression's Structure
3:03
Substitute a Number Without Changing the Expression's Structure
You'll learn: Replace the letter with a number but keep every operation of the expression unchanged.
How Does an Expression's Value Change with Its Input?
3:17
How Does an Expression's Value Change with Its Input?
You'll learn: Substitute different inputs to see how the value of an expression changes.

Next topic

Angles at an intersection

2

Why Do Adjacent Angles on a Line Add to 180°?
3:04
Why Do Adjacent Angles on a Line Add to 180°?
You'll learn: Adjacent angles that form a straight line together make 180°.
Why Are Vertically Opposite Angles Equal?
3:10
Why Are Vertically Opposite Angles Equal?
You'll learn: A single equality proof needs the linear-pair deductions to remain visible.

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Geometric facts versus measurements

1

Why Does Measuring a Diagram Not Prove a Geometric Fact?
3:38
Why Does Measuring a Diagram Not Prove a Geometric Fact?
You'll learn: Measuring a drawing can suggest a fact, but drawings are imperfect, so a proof is needed.

Next topic

Perpendicular lines

1

Why Do Four Equal Intersection Angles Make Perpendicular Lines?
3:22
Why Do Four Equal Intersection Angles Make Perpendicular Lines?
You'll learn: If four angles at an intersection are equal, each is 90°, so the lines are perpendicular.

Next topic

Parallel lines and segment intersections

2

When Do Segments Meet—and What Happens If We Extend Them?
3:22
When Do Segments Meet—and What Happens If We Extend Them?
You'll learn: Segments can meet at endpoints, midpoints or interior points, and extending them can create new meeting points.
Why Must Parallel Lines Lie in the Same Plane?
3:15
Why Must Parallel Lines Lie in the Same Plane?
You'll learn: Lines that never meet but lie in different planes are not parallel; parallel lines must share a plane.

Next topic

Lines through paper folding

1

Make Parallel and Perpendicular Creases by Folding
3:27
Make Parallel and Perpendicular Creases by Folding
You'll learn: Fold paper to make parallel and perpendicular creases and spot the repeating pattern.