Mensuration 2D chapter में हम उन आकृतियों के क्षेत्रफल (Area) और परिमाप (Perimeter) सीखते हैं जो रोज़मर्रा के जीवन में दिखती हैं—Square, Rectangle, Triangle, Circle आदि। Delhi Police Exam में **2–3 direct formula-based** सवाल आते हैं। यदि formula याद है → 10 seconds में answer।
| Shape | Area | Perimeter |
|---|---|---|
| Square (वर्ग) | a² | 4a |
| Rectangle (आयत) | L×B | 2(L+B) |
| Triangle (त्रिभुज) | ½ × base × height | a+b+c |
| Right Triangle | ½ × perpendicular × base | Pythagoras: h² = p² + b² |
| Circle (वृत्त) | πr² | 2πr |
| Parallelogram (समांतर चतुर्भुज) | b × h | 2(a+b) |
| Trapezium (समलम्ब) | ½ (a + b)h | a+b+c+d |
| Rhombus (समचतुर्भुज) | ½ (d₁ × d₂) | 4a |
Example 1: Side of square = 12 cm. Area = 12² = 144 cm²
Example 2: Rectangle: L=15, B=10 Area = 150 Perimeter = 50
Example 3: Circle radius = 7 Area = 22/7 × 49 = 154
Example 4: Triangle: base=20, height=8 Area = ½×20×8 = 80
Example 5: Parallelogram: base=10, height=6 Area = 60
Example 6: Rhombus diagonals = 10, 12 Area = ½×10×12 = 60
Example 7: Trapezium: parallel sides 10, 16, height 8 Area = ½(10+16)×8 = 104
Example 8: Circle: diameter=14 → radius=7 Perimeter = 2πr = 44
A circular garden has radius 21 m. Find area & fencing cost if fencing is ₹20 per meter.
Area = πr² = 22/7 × 441 = 1386 m²
Perimeter = 2πr = 2 × 22/7 × 21 = 132 m
Fencing cost = 132 × 20 = ₹2640
💡 Motivation: Formula याद, दिमाग शांत — Mensuration बन जाता है सबसे आसान chapter! 🚓🔥