3. Write down the measures of
(a) some acute angles.
(b) some obtuse angles.
(give at least two examples of each).
2. Say True or False :
(a) The measure of an acute angle < 90°.
(b) The measure of an obtuse angle < 90°.
(c) The measure of a reflex angle > 180°.
(d) The measure of one complete revolution = 360°.
(e) If m A∠ = 53° and m B∠ = 35°, then m A∠ > m B.
1. What is the measure of (i) a right angle? (ii) a straight angle?
2. Classify each one of the following angles as right, straight, acute, obtuse or reflex :
1. Match the following :
(i) Straight angle
(a) Less than one-fourth of a revolution
(ii) Right angle
(b) More than half a revolution
(iii) Acute angle
(c) Half of a revolution
(iv) Obtuse angle
(d) One-fourth of a revolution
(v) Reflex angle
(e) Between and of a revolution
(f) One complete revolution
7. Where will the hour hand of a clock stop if it starts
(a) from 6 and turns through 1 right angle?
(b) from 8 and turns through 2 right angles?
(c) from 10 and turns through 3 right angles?
(d) from 7 and turns through 2 straight angles?
6. How many right angles do you make if you start facing
(a) south and turn clockwise to west?
(b) north and turn anti-clockwise to east?
(c) west and turn to west?
(d) south and turn to north?
5. Find the number of right angles turned through by the hour hand of a clock when it goes from
(a) 3 to 6 (b) 2 to 8 (c) 5 to 11
(d) 10 to 1 (e) 12 to 9 (f) 12 to 6
4. What part of a revolution have you turned through if you stand facing
(a) east and turn clockwise to face north?
(b) south and turn clockwise to face east?
(c) west and turn clockwise to face east?
3. Which direction will you face if you start facing
(a) east and make of a revolution clockwise?
(b) east and make of a revolution clockwise?
(c) west and make of a revolution anti-clockwise?
(d) south and make one full revolution?
(Should we specify clockwise or anti-clockwise for this last question? Why not?)
2. Where will the hand of a clock stop if it
(a) starts at 12 and makes of a revolution, clockwise?
(b) starts at 2 and makes of a revolution, clockwise?
(c) starts at 5 and makes of a revolution, clockwise?
(d) starts at 5 and makes of a revolution, clockwise?
1. What fraction of a clockwise revolution does the hour hand of a clock turn through, when it goes from
(a) 3 to 9 (b) 4 to 7 (c) 7 to 10
(d) 12 to 9 (e) 1 to 10 (f) 6 to 3
7. Draw five triangles and measure their sides. Check in each case, if the sum of the lengths of any two sides is always less than the third side.
6. If B is the mid point of AC and C is the mid point of BD, where A,B,C,D lie on a straight line, say why AB = CD?
5. Verify, whether D is the mid point of AG .
4. If A,B,C are three points on a line such that AB = 5 cm, BC = 3 cm and AC = 8 cm, which one of them lies between the other two?
3. Draw any line segment, say AB. Take any point C lying in between A and B. Measure the lengths of AB, BC and AC. Is AB = AC + CB?
[Note : If A,B,C are any three points on a line such that AC + CB = AB, then we can be sure that C lies between A and B.]
2. Why is it better to use a divider than a ruler, while measuring the length of a line segment?
1. What is the disadvantage in comparing line segments by mere observation?