8th Math NCERT Chapter 3
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Here are the important topics from the chapter on "Understanding Quadrilaterals" along with a brief summary for each:
1. Convex and Concave Polygons:
– Summary: Convex polygons have no portions of their diagonals in their exteriors, while concave polygons have line segments joining points that lie partly outside the shape7.
2. Regular and Irregular Polygons:
– Summary: Regular polygons are both equiangular and equilateral, like a square, while irregular polygons do not have all sides and angles equal7.
3. Sum of the Exterior Angles of a Polygon:
– Summary: The sum of the exterior angles of a polygon is always 360 degrees, regardless of the number of sides7.
4. Types of Quadrilaterals:
– Summary: Quadrilaterals have special names based on their sides and angles, such as trapeziums which have a pair of parallel sides, kites with two pairs of equal sides, and parallelograms which have opposite sides parallel7.
Describe in your own words the difference between convex polygons and concave polygons.
Convex polygons have no portions of their diagonals in their exteriors, and any line segment joining any two different points in the interior of the polygon lies wholly in its interior. Concave polygons do not possess this property.
Define a regular polygon and provide an example of a regular polygon with 3 sides.
A regular polygon is both 'equiangular' and 'equilateral'. An example of a regular polygon with 3 sides is an equilateral triangle.
Calculate the sum of the measures of the exterior angles of a regular hexagon. Are all the exterior angles of a regular hexagon equal? Why?
The sum of the measures of the exterior angles of a regular hexagon is 360 degrees. All the exterior angles of a regular hexagon are equal because each exterior angle of a regular polygon is equal.
How many sides does a regular polygon have if each of its interior angles measures 165 degrees?
A regular polygon has 24 sides if each of its interior angles measures 165 degrees. This is because the formula to find the number of sides in a regular polygon is 360 / (180 – interior angle).
Explain what a trapezium is and how it differs from other quadrilaterals.
A trapezium is a quadrilateral with a pair of parallel sides. This distinguishes it from other quadrilaterals where all sides are not parallel. Trapeziums have only one pair of parallel sides while other quadrilaterals do not necessarily have parallel sides.
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