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Chapter 8 of 12
Flashcards

Heron's Formula

Karnataka Board · Class 9 · Mathematics

Flashcards for Heron's Formula — Karnataka Board Class 9 Mathematics. Quick Q&A cards covering key concepts, definitions, and formulas.

45 questions20 flashcards4 concepts
20 Flashcards
Card 1Basic Heron's Formula Application

Find the area of a triangle with sides 3 cm, 4 cm, and 5 cm using Heron's formula.

Answer

Step 1: Calculate semi-perimeter s = (a+b+c)/2 = (3+4+5)/2 = 6 cm Step 2: Apply Heron's formula: Area = √[s(s-a)(s-b)(s-c)] Step 3: Substitute values: Area = √[6(6-3)(6-4)(6-5)] = √[6×3×2×1] = √36 = 6

Card 2Practical Applications

A triangular plot has sides 13 m, 14 m, and 15 m. Find its area.

Answer

Step 1: s = (13+14+15)/2 = 42/2 = 21 m Step 2: s-a = 21-13 = 8 m, s-b = 21-14 = 7 m, s-c = 21-15 = 6 m Step 3: Area = √[21×8×7×6] = √[7056] = 84 m² Answer: 84 m²

Card 3Special Triangles

Find the area of an equilateral triangle with side 6 cm using Heron's formula.

Answer

Step 1: For equilateral triangle, all sides = 6 cm Step 2: s = (6+6+6)/2 = 9 cm Step 3: s-a = s-b = s-c = 9-6 = 3 cm Step 4: Area = √[9×3×3×3] = √[243] = 9√3 cm² ≈ 15.59 cm² Answer: 9√3 cm²

Card 4Ratio Problems

The sides of a triangle are in ratio 3:4:5 and perimeter is 24 cm. Find the area.

Answer

Step 1: Let sides be 3x, 4x, 5x. Perimeter = 3x+4x+5x = 12x = 24 Step 2: x = 2, so sides are 6 cm, 8 cm, 10 cm Step 3: s = 24/2 = 12 cm Step 4: Area = √[12×(12-6)×(12-8)×(12-10)] = √[12×6×4×2] = √576

Card 5Formula Understanding

State Heron's formula and explain what each variable represents.

Answer

Heron's Formula: Area = √[s(s-a)(s-b)(s-c)] Where: a, b, c = sides of triangle s = semi-perimeter = (a+b+c)/2 Example: For triangle with sides 5,12,13: s = 15, Area = √[15×10×3×2] = 30 units²

Card 6Verification Methods

Find the area of triangle with sides 7 cm, 24 cm, and 25 cm. Verify it's a right triangle.

Answer

Step 1: Check if right triangle: 7² + 24² = 49 + 576 = 625 = 25² ✓ (Right triangle) Step 2: s = (7+24+25)/2 = 28 cm Step 3: Area = √[28×21×4×3] = √[7056] = 84 cm² Verification: Area = ½×7×24 = 84 cm²

Card 7Given Perimeter Problems

A triangle has perimeter 30 cm. Two sides are 8 cm and 12 cm. Find the area.

Answer

Step 1: Third side = 30 - 8 - 12 = 10 cm Step 2: Check triangle inequality: 8+10 > 12 ✓, 8+12 > 10 ✓, 10+12 > 8 ✓ Step 3: s = 30/2 = 15 cm Step 4: Area = √[15×(15-8)×(15-12)×(15-10)] = √[15×7×3×5] = √

Card 8When to Use Heron's Formula

When should you use Heron's formula instead of ½×base×height?

Answer

Use Heron's formula when: • You know all three sides but not the height • Finding height is difficult or impossible • Working with scalene triangles Example: Triangle park with sides 40m, 32m, 24m He

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Frequently Asked Questions

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Heron's Formula covers several key topics that are frequently asked in Karnataka Board Class 9 board exams. Focus on the core concepts listed on this page and practise related questions to build confidence.

Start by understanding all key concepts. Practise previous year questions from this chapter. Revise formulas and definitions regularly. Use flashcards for quick revision before the exam.

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Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.