📖Definition
Perimeter is the total distance around the outside of a two-dimensional shape. It is found by adding up the lengths of all the sides. For circles, the perimeter is called the circumference. Perimeter is measured in linear units (cm, m, in, ft, etc.).
📐Formula
For rectangles, add length and width then multiply by 2. For squares, multiply one side by 4. For circles, the circumference equals 2 times pi times the radius.
📝Step-by-Step Guide
Identify All Sides
Count how many sides the shape has and find the length of each side.
Add All Side Lengths
For polygons, add up all the side lengths. Make sure all measurements use the same unit.
Use Formulas for Regular Shapes
For rectangles: P = 2l + 2w or P = 2(l + w). For squares: P = 4s.
For Circles Use Circumference
Circumference = 2πr or πd, where r is radius and d is diameter.
⚠️Common Mistakes to Avoid
- Confusing perimeter with area
- Forgetting to include all sides
- Using square units instead of linear units
- For circles, confusing radius with diameter
- Not converting all measurements to the same unit first
✏️Practice Problems
Find the perimeter of a rectangle with length 7 cm and width 4 cm
Answer: 22 cm
Find the circumference of a circle with radius 5 m (use π = 3.14)
Answer: 31.4 m
A rectangle has perimeter 36 cm. If the length is twice the width, find the dimensions.
Answer: Length = 12 cm, Width = 6 cm
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