Lines and Angles – Class 9/Maths.

Chapter 6 of NCERT/CBSE Class 9 Maths is about Lines and Angles. Here you can find out practice problems for this chapter.

CBSE CLASS 9 MATHEMATICS
Lines and Angles – Chapter 6 /Sample Papers.
Fill in the blanks:

1. An angle whose measure is less than 90 degree is called an ————-
2. An angle whose measure is more than 90 degree is called an————–
3. An angle whose measure is 90 degree is called a ——-
4. The measure of a straight angle is ————degree.
5. An angle whose measure is 360 degree is called a ————–
6. An angle whose measure is more than 180 degree but less than 360 degree is called ——-
7. Two angles whose sum is 90 degree are called —————–
8. Two angles whose sum is 180 degree are called ————-
9. If three or more points lie on the same line, they are called —————
10. When the sum of two adjacent angles is 180 degree, then they are called a ————–of angles.
    Answer the following questions:
11. Find the supplement of ¾ of 120 degree.
12. If (2x – 35) and (x + 5) are complementary angles, find the angles.
13. Two supplementary angles are in the ratio 1:2, find the angles.
14. If a transversal intersects two parallel lines, then
    i) each pair of ———— angles is equal
    ii) each pair of ———- angles is equal
    iii) each pair of interior angles on the same side of the transversal is ————–
15. If the angles of a triangle are in the ratio 1:2:3, then find the measures of the three angles?

ANSWERS:

1. Acute angle
2. Obtuse angle
3. Right angle
4. 180
5. Complete angle
6. Reflex
7. Complementary
8. Supplementary
9. Collinear points
10. Linear pair
11. ¾ of 120 = ¾ x 120 = 90 degree
    Supplement of 90 degree is 90 degree itself.
12. Given (2x – 35) and (x + 5) are complementary angles. So their sum must be 90 degree.
    2x – 35 + x + 5 = 90
    3x – 30 = 90
    3x = 90 + 30
    3x = 120
    x = 120/3 = 40
    So the angles are 2x -35 = 2 x 40 –35 = 80 – 35 = 45 degree
    x + 5 = 40 + 5 = 45 degree.
13. Let the angles be x and 2x
    Since it is supplementary, their sum must be 180 degree.
    Therefore, x + 2x = 180
    3x = 180
    x = 180/3 = 60
    So the two angles are 60 degree and 120 degree.
14. i) corresponding angles
    ii) Alternate interior angles
    iii) Supplementary
15. Let the three angles be x, 2x and 3x.
    By Angle sum property of triangles, x + 2x + 3x = 180
    6x = 180
    x= 180/6 = 30 degree
    So the three angles are 30, 60 and 90 degrees.