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Revision Notes: Area Theorems | Mathematics Class 9 ICSE PDF Download

  • The amount of surface enclosed by the boundary of a plane closed figure is called its area and is measure in squared units. 
  • A diagonal of a parallelogram divides it into two congruent triangles i.e. two triangles of equal area. 
  • Parallelograms between the same base and between the same parallels are equal in area. 
  • A parallelogram and a rectangle on the same base and between the same parallels are equal in area.
  • Parallelograms with equal bases and between the same parallels are equal in area. 
  • If a triangle and a parallelogram are on the same base and between the same parallels, then the area of the triangle is equal to half area of the parallelogram.
  • Triangles on the same base and between the same parallels are equal in area. 
  • Triangles with equal bases and between the same parallels are equal in area. 
  • Triangles with equal areas and lying on the same or equal bases have equal altitudes. 
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FAQs on Revision Notes: Area Theorems - Mathematics Class 9 ICSE

1. What are the main area theorems covered in Class 9 mathematics?
Ans. In Class 9 mathematics, the main area theorems include the area of triangles, quadrilaterals, and circles. The key concepts involve understanding how to calculate the area using different formulas, such as the area of a triangle (1/2 * base * height), the area of a rectangle (length * breadth), and the area of a circle (π * radius²).
2. How do you find the area of a triangle using the base and height?
Ans. To find the area of a triangle, you can use the formula: Area = 1/2 * base * height. You need to measure the length of the base and the perpendicular height from the base to the opposite vertex. Multiply these two values and then divide by 2 to get the area.
3. What is the formula for calculating the area of a circle in Class 9?
Ans. The formula for calculating the area of a circle is given by Area = π * radius². Here, 'π' is a constant approximately equal to 3.14, and 'radius' is the distance from the center of the circle to any point on its circumference.
4. Can you explain how to find the area of a quadrilateral?
Ans. The area of a quadrilateral can be found using different methods depending on the type of quadrilateral. For a rectangle, use Area = length * breadth. For a square, use Area = side². For irregular quadrilaterals, you can divide it into simpler shapes (like triangles or rectangles), find their areas, and then sum them up.
5. Why is it important to understand area theorems in Class 9?
Ans. Understanding area theorems in Class 9 is crucial because they form the foundation for more advanced mathematical concepts. These theorems are not only used in geometry but also in real-life applications such as architecture, engineering, and various fields where spatial measurements are required. Mastery of these concepts helps students develop critical thinking and problem-solving skills.
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