Understanding Quadrilaterals – Class 8.

Chapter 3 of NCERT/CBSE Class 8 Mathematics is about Understanding Quadrilaterals. Here in this lesson you can find out practice problems from this chapter.

CBSE CLASS 8 MATHEMATICS
Understanding Quadrilaterals – Chapter 3 / Model Questions.
Fill in the blanks:

1. A 10 sided polygon is known as ————-
2. A line segment connecting two non-consecutive vertices of a polygon is called ———-
3. The name of a regular polygon with 4 sides is ———–
4. The number of diagonals a regular hexagon have ————
   Answer the following:
5. In a parallelogram ABCD, opposite sides are given by 4x – 4 and x -1. Find the value of x?
6. Find the sum of all the exterior angles of a triangle?
7. In a triangle PQR, the three angles are given by (x + 5), (x + 10) and (3x + 15). Find the value of x?
8. Three angles of a quadrilateral are 35, 65 and 128 degrees. Find the measure of the fourth angle?
9. In a parallelogram ABCD, if one angle is 70 degree, find all the other angles?
10. Find the perimeter of a parallelogram whose sides are given by 6 cm and 12 cm?

ANSWERS:

1. Decagon
2. Diagonals
3. Square or Rhombus
4. 9 sides
5. Since the opposite sides of a parallelogram are of equal measure,
   4x – 4 = x – 1
   4x – x = -1 + 4
   3x = 3
   x = 1.
6. We know that the sum of the measures of the external angles of any polygon is 360 degree. Therefore, sum of all the exterior angles of a triangle is 360 degree.
7. By angle sum property of triangles, sum of the three angles = 180 degree
   x + 5 + x + 10 + 3x + 15 = 180
   5x + 30 = 180
   5x = 180 – 30 = 150
   x = 150 / 5 = 30
8. We know that sum of four angles of a quadrilateral is 360 degree.
   Let the fourth angle be x and the other three angles are 35, 65 and 128.
   Therefore, 35 + 65 + 128 + x = 360
   228 + x = 360
   x = 132
   Therefore, the measure of fourth angle is 132 degree.
9. Since the opposite angles of a parallelogram are equal, the measures of 2 angles are 70 degree. Also adjacent angles of a parallelogram are supplementary. Therefore, the other two angles are 110 degree each.
10. In a parallelogram the opposite sides have same length.
    So perimeter = 6 + 12 + 6 + 12 = 36 cm