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Angles
It is common knowledge that the sum of the angles in a triangle is 180° but how about in polygons with a greater numbers of angles? If we are given a convex polygon with n sides and S is the sum of the measures of the interior angles then S = 180(n - 2).
Example
Find the sum of the measures of the interior angles in an octagon.
The octagon has 8 sides and we plug this value into our formula:
S = 180(8 - 2) = 1080°
Hence the sum of the measures of the interior angles in an octagon is 1080°.
Another thing with convex polygons is that the sum of the measures of the exterior angles is always 360°
Quadrilaterals - General Geometry | Additional Topics for IIT JAM Mathematics
m∠A + m∠B + m∠C + m∠D + m∠E + m∠F = 360

Properties of parallelograms
One special kind of polygons is called a parallelogram. It is a quadrilateral where both pairs of opposite sides are parallel.
Quadrilaterals - General Geometry | Additional Topics for IIT JAM Mathematics
There are six important properties of parallelograms to know:
1. Opposite sides are congruent (AB = DC).
2. Opposite angels are congruent (D = B).
3. Consecutive angles are supplementary (A + D = 180°).
4. If one angle is right, then all angles are right.
5. The diagonals of a parallelogram bisect each other.
6. Each diagonal of a parallelogram separates it into two congruent triangles.
Quadrilaterals - General Geometry | Additional Topics for IIT JAM Mathematics
△ACD ≅ △ABC
If we have a parallelogram where all sides are congruent then we have what is called a rhombus. The properties of parallelograms can be applied on rhombi.
If we have a quadrilateral where one pair and only one pair of sides are parallel then we have what is called a trapezoid. The parallel sides are called bases while the nonparallel sides are called legs. If the legs are congruent we have what is called an isosceles trapezoid.
Quadrilaterals - General Geometry | Additional Topics for IIT JAM Mathematics
In an isosceles trapezoid the diagonals are always congruent. The median of a trapezoid is parallel to the bases and is one-half of the sum of measures of the bases.
Quadrilaterals - General Geometry | Additional Topics for IIT JAM Mathematics
Quadrilaterals - General Geometry | Additional Topics for IIT JAM Mathematics

The document Quadrilaterals - General Geometry | Additional Topics for IIT JAM Mathematics is a part of the Mathematics Course Additional Topics for IIT JAM Mathematics.
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FAQs on Quadrilaterals - General Geometry - Additional Topics for IIT JAM Mathematics

1. What are the properties of a quadrilateral?
Ans. A quadrilateral is a polygon with four sides and four vertices. The properties of a quadrilateral include: - The sum of the interior angles is always equal to 360 degrees. - Opposite angles are equal. - The opposite sides are parallel in a parallelogram. - The diagonals bisect each other in a parallelogram.
2. What are the types of quadrilaterals?
Ans. There are different types of quadrilaterals, including: - Parallelogram: A quadrilateral with both pairs of opposite sides parallel. - Rectangle: A parallelogram with all angles equal to 90 degrees. - Square: A parallelogram with all sides equal in length and all angles equal to 90 degrees. - Rhombus: A parallelogram with all sides equal in length. - Trapezoid: A quadrilateral with one pair of opposite sides parallel.
3. How do you find the area of a quadrilateral?
Ans. The area of a quadrilateral can be found using different formulas depending on the type of quadrilateral: - Parallelogram: The area is given by base times height. - Rectangle: The area is given by length times width. - Square: The area is given by side length squared. - Rhombus: The area is given by the product of the diagonals divided by 2. - Trapezoid: The area is given by the average of the lengths of the parallel sides multiplied by the height.
4. Can a quadrilateral have all sides equal in length but not all angles equal?
Ans. No, a quadrilateral with all sides equal in length is a special type called a square. In a square, all angles are also equal to 90 degrees. If a quadrilateral has all sides equal but not all angles equal, it would be a rhombus.
5. What is the sum of the angles in a quadrilateral?
Ans. The sum of the angles in a quadrilateral is always equal to 360 degrees. This means that if you add up all the interior angles of a quadrilateral, the total sum will be 360 degrees.
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