Area and perimeter

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Side A

Side B

❓ What are area and perimeter

Area (S) is how much space a figure occupies on a plane, measured in square units: cm², m², km², etc.

Perimeter (P) is the sum of all side lengths of a closed figure — the length of its boundary. For a circle, circumference (L) is used instead of perimeter.

Supports rectangle, square, circle and triangle. For a triangle by base and height only area is computed — perimeter needs all three sides.

📐 Formulas

Rectangle

S = a × b

P = 2 × (a + b)

Square

S = a²

P = 4 × a

Circle

S = π × R²

L = 2 × π × R

Triangle

S = ½ × base × height

P = a + b + c (all three sides needed)

💡 Examples

Rectangle: a = 5, b = 3

S = 5 × 3 = 15, P = 2 × (5 + 3) = 16

Square: a = 4

S = 4² = 16, P = 4 × 4 = 16

Circle: R = 3

S = π × 3² ≈ 28.27, L = 2 × π × 3 ≈ 18.85

Triangle: base = 6, height = 4

S = ½ × 6 × 4 = 12

✅ Tips

Use the same units for all sides — metres with metres, centimetres with centimetres.
For a rectangle, a and b are length and width — any positive numbers.
A circle’s perimeter is called circumference; π ≈ 3.14159.
Triangle area via base and height works for any triangle if the height is to that base.