Chapter 7 of 9
Revision Notes
Mensuration — Revision Notes
Tamil Nadu Board · Class 9 · Mathematics
Mensuration revision notes for Tamil Nadu Board Class 9 Mathematics: 4 topics in quick points. Part of the Tamil Nadu Board Class 9 Mathematics syllabus.
44 questions25 flashcards6 formulas & key relations5 concepts
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Key Topics to Revise
1
7.1 - 7.2: Heron's Formula and Triangle Areas
- Heron's Formula is used when the height of a triangle is unknown but all three sides are given
- Semi-perimeter (s) is half the perimeter: s = (a + b + c)/2
- Area = √[s(s-a)(s-b)(s-c)] square units
2
7.3: Heron's Formula for Quadrilaterals
- To find the area of a quadrilateral using Heron's formula, divide it into two triangles using a diagonal
- Method: Draw a diagonal to create two triangles, calculate area of each using Heron's formula, then add them
- Area of Quadrilateral ABCD = Area of Triangle ABC + Area of Triangle ACD (when divided by diagonal AC)
3
7.4: Surface Area of Cuboids and Cubes
- Cuboid: A 3D solid with 6 rectangular faces, 12 edges, and 8 vertices; defined by length (l), breadth (b), and height (h)
- Cube: Special cuboid where l = b = h; all faces are squares
- Total Surface Area (TSA): Sum of areas of all 6 faces
4
7.5: Volume of Cuboids and Cubes
- Volume: The measure of space occupied by a 3D solid, expressed in cubic units (cm³, m³, etc.)
- Volume = Base Area × Height
- For Cuboid: V = l × b × h (length × breadth × height)
Get complete notes with diagrams and examples
Full NotesKey Concepts
Heron's formula allows calculating the areaThe semiA quadrilateral can be divided intoA cuboid is a threeTSA is the sum of areas
Frequently Asked Questions
What are the important topics in Mensuration for Tamil Nadu Board Class 9 Mathematics?
Key topics in Mensuration include 1 - 7.2: Heron's Formula and Triangle Areas, 3: Heron's Formula for Quadrilaterals, 4: Surface Area of Cuboids and Cubes, 5: Volume of Cuboids and Cubes. Study these first, then practise questions on each for Class 9 exams.
How should I revise Mensuration for Class 9 exams?
Learn the core ideas first, then work through the 44 practice questions on Mensuration. Revise definitions regularly and use flashcards for quick recall before the exam.
Sources & Official References
Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.
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