Mathematics
Grade 8
15 min
Write variable expressions from diagram
Write variable expressions from diagram
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1
Introduction & Learning Objectives
Learning Objectives
Identify unknown quantities in a given diagram and assign appropriate variables.
Translate visual information from geometric diagrams into algebraic relationships.
Write variable expressions for the perimeter of various polygons shown in diagrams.
Write variable expressions for the area of rectangles and squares depicted in diagrams.
Write variable expressions for lengths or quantities based on parts of a diagram.
Simplify variable expressions derived from diagrams by combining like terms.
Ever wondered how architects or engineers describe the size of a building or a park without knowing exact measurements? 📐 They use algebra!
In this lesson, you'll learn how to translate visual information from diagrams into mathematical language using variables a...
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Key Concepts & Vocabulary
TermDefinitionExample
VariableA symbol, usually a letter (like x, y, or w), that represents an unknown or changing quantity.In a diagram, if the length of a side is unknown, we might label it 'x'.
Algebraic ExpressionA mathematical phrase that contains numbers, variables, and operation symbols (like +, -, ×, ÷), but does not contain an equality sign (=).If a side is 'x' and another is 'x + 5', their sum is the expression 'x + (x + 5)'.
DiagramA visual representation of a situation, often showing geometric shapes, their parts, and sometimes their known or unknown dimensions.A drawing of a rectangle with sides labeled 'length' and 'width'.
PerimeterThe total distance around the outside of a two-dimensional shape. It is found by add...
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Core Formulas
Assigning Variables to Unknowns
Identify any unknown lengths or quantities in the diagram and assign a unique variable (e.g., $x$, $y$, $w$) to each distinct unknown.
If two parts of a diagram are stated or shown to be equal, they should be represented by the same variable. If they are different, use different variables.
Translating Geometric Relationships
Use the properties of the shapes (e.g., opposite sides of a rectangle are equal, total length is the sum of its parts) to express other dimensions in terms of the assigned variables.
For example, if a total length is 10 and one part is $x$, the other part is $10 - x$. If a side is twice another side $y$, it's $2y$.
Formulating Expressions for Perimeter
To write an expression for the perimeter ($P$) of a polygon,...
5 more steps in this tutorial
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Challenging
A diagram shows a rectangle. The width is given as 'w'. The length is described in relation to the width: '4 more than twice the width'. Which simplified expression represents the perimeter of the rectangle in terms of 'w'?
A.3w + 4
B.2w² + 4w
C.6w + 8
D.4w + 8
Challenging
A diagram shows four identical squares with side length 'x' arranged in a 2x2 grid to form a larger square. Which expression represents the perimeter of this new, larger square?
A.16x
B.8x
C.4x²
D.16x²
Challenging
A diagram shows a large square with side length 'S'. A smaller square with side length 's' is cut from one corner. This leaves an L-shaped region. Which expression represents the perimeter of this L-shaped region?
A.4S - 4s
B.S² - s²
C.4S
D.4S + 2s
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