Mathematics Grade 7 15 min

Perimeter (Advanced using algebra)

Perimeter (Advanced using algebra)

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Introduction & Learning Objectives

Learning Objectives Write algebraic expressions for the perimeter of various polygons. Formulate and solve linear equations to find unknown side lengths given the perimeter of a shape. Apply perimeter concepts to solve real-world problems involving algebraic expressions. Calculate the actual dimensions of a shape after solving for a variable. Distinguish between perimeter and area in problem-solving contexts involving algebraic terms. Solve problems involving composite shapes where side lengths are expressed algebraically. Ever wondered how much fencing you'd need for a garden shaped like an irregular polygon, where some sides are unknown? 🏡 Let's find out how algebra helps us solve these tricky perimeter puzzles! In this lesson, you'll dive deeper into calc...
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Key Concepts & Vocabulary

TermDefinitionExample PerimeterThe total distance around the outside of a two-dimensional shape. It is found by adding the lengths of all its sides.If a square has sides of 5 cm, its perimeter is 5 + 5 + 5 + 5 = 20 cm. VariableA symbol, usually a letter (like x, y, or w), that represents an unknown number or quantity in a mathematical expression or equation.In the expression `2x + 5`, 'x' is the variable representing an unknown value. Algebraic ExpressionA mathematical phrase that can contain numbers, variables, and operation symbols (like +, -, ×, ÷) but does not contain an equals sign.`3w + 2L` is an algebraic expression that could represent the perimeter of a rectangle. EquationA mathematical statement that shows two expressions are equal, typically containing an equals sign...
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Core Formulas

Perimeter of Any Polygon $P = s_1 + s_2 + s_3 + ... + s_n$ To find the perimeter (P) of any polygon, add the lengths of all its individual sides ($s_1, s_2$, etc.). This is the fundamental rule for setting up algebraic expressions for perimeter. Perimeter of a Rectangle $P = 2(l + w)$ or $P = 2l + 2w$ Use this formula when dealing with rectangles, where 'l' is the length and 'w' is the width. If length or width are given as algebraic expressions, substitute them into the formula. Perimeter of a Square $P = 4s$ Use this formula for squares, where 's' represents the length of one side. Since all four sides of a square are equal, you can simply multiply the side length by 4. If 's' is an algebraic expression, multiply the entire e...

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Sample Practice Questions

Challenging
A composite shape is formed by a square with side length `x` attached to one side of an equilateral triangle, also with side length `x`. The shape resembles a house. If the total perimeter of this composite shape is 50 cm, what is the value of `x`?
A.8
B.10
C.12.5
D.25
Challenging
A quadrilateral has a perimeter represented by the expression `15y - 8`. Three of its sides are `2y`, `3y + 5`, and `4y - 10`. What is the expression for the fourth side?
A.6y - 3
B.9y - 5
C.6y + 3
D.24y - 13
Challenging
A rectangular field has a width of `x` meters and a length of `(x + 6)` meters. The perimeter is 44 meters. What is the AREA of the field?
A.8 sq meters
B.14 sq meters
C.112 sq meters
D.484 sq meters

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