Mensuration of Plane Figures
Plane figures include triangle, circle, square, rectangle, and parallelogram.

1. Triangle
Perimeter: a + b + c
Area: 1/2 × bh
2. Circle
Circumference: 2πr
Area: πr2
3. Square
Perimeter: 4a
Area: a2
4. Rectangle
Perimeter: 2(l + b)
Area: l × b
5. Parallelogram
Perimeter: 2(a + b)
Area: bh