Perimeter and Area (NCERT Ch. 11)

• Find the perimeter and area of squares and rectangles (recap and extend from Class 6).
• Find the area of a right triangle and a general triangle (using base and height).
• Find the area and circumference of a circle.

1. Area of a triangle = (1/2) x base x height.
2. Circumference of a circle = 2 x π x radius (or π x diameter).
3. Area of a circle = π x radius².
4. Use π ≈ 22/7 or 3.14 for calculations unless stated otherwise.
5. Conversion of units: 1 m = 100 cm; 1 sq m = 10,000 sq cm.

Find the area of a circle with radius 7 cm. (use π = 22/7)

Area = π x r² = 22/7 x 7 x 7 = 22 x 7 = 154 sq cm

• Using diameter instead of radius in the area formula (Area uses radius, not diameter).
• Forgetting the 1/2 factor when calculating triangle area.
• Mixing units (cm and m) without converting first.

• Find the circumference of a circle with radius 14 cm (use π = 22/7).
• Find the area of a triangle with base 10 cm and height 6 cm.

Open the Practice tab for graded questions on Perimeter and Area (NCERT Ch. 11).