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🔵Find Perimeter by Adding Sides
Perimeter is the total distance around the outside of a shape.
Perimeter = sum of all side lengths
- Rectangle: P = 2 x (length + width)
- Square: P = 4 x side
- Any shape: add up all sides
👀 See a worked example
Rectangle: length 7 m, width 4 m. Find the perimeter.
P = 7+4+7+4 = 22 m. Or use formula: P = 2 x (7+4) = 2 x 11 = 22 m.
Square: side 9 cm. Find the perimeter.
P = 4 x 9 = 36 cm. A square has 4 equal sides.
Triangle: sides 3 cm, 5 cm, 6 cm. Find the perimeter.
P = 3 + 5 + 6 = 14 cm. Add all 3 sides.
🤖 Vidi's Key Points
- Perimeter = total distance around the shape.
- Rectangle: P = 2x(L+W). Square: P = 4 x side.
- For any shape: just add up all side lengths.
🟢Find the Missing Side Given Perimeter
If you know the perimeter and some side lengths, subtract to find the missing side.
Missing side = Perimeter - sum of known sides
For rectangles: Perimeter = 2 x (Length + Width), so Length + Width = Perimeter / 2.
👀 See a worked example
Square perimeter is 36 cm. What is each side?
Square side = Perimeter / 4 = 36 / 4 = 9 cm.
Rectangle perimeter 30 m, length 10 m. Find the width.
P = 2(L+W). 30 = 2(10+W). 15 = 10+W. W = 5 m.
Triangle perimeter 21 cm. Two sides are 7 cm and 8 cm. Find the third side.
Third side = 21 - 7 - 8 = 6 cm.
🤖 Vidi's Key Points
- Missing side = Perimeter - all known sides.
- For rectangles: L+W = P/2, then find the unknown.
- Always check your answer by recalculating the full perimeter.
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