EXERCISE 5.4
1) What is the measure of
(a) A right angle (b) A straight angle.
Ans : (a) 90˚ (b) 180˚
2) Say whether true or false :-
(a) The measure of an acute angle < 90 ˚
(b) The measure of an obtuse angle< 90˚
(c) The measure of an 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
Ans : (a) True (b) False (c) True (d) True (e) True
3) Write down the measures of: (give 2 example of each)
(a) Some acute angles.
Ans : 30˚ , 40˚.
(b) Some obtuse angles.
Ans : 120˚ , 157˚
4) Measure the angles given below,using the protector and write down the measure
(a) 45˚ (b) 120˚ (c) 90˚ (d) 60˚, 130˚, 90˚
5) Which angle has a large measure?
(1) First estimate and then measure.
Ans : Measure of angle A = 40 ˚
Measure of angle B = 68˚
∠B has a larger measure than ∠A
6) From these two angles which has larger measure? Estimate and then confirm by measuring them.
Ans : The angle shown in the second figure looks the larger angle. This can be confirmed by measuring both the angles.
Measure of first angle = 45˚
Measure of second angle = 68˚
7) Fill in the blanks with acute , obtuse , right or straight.
(a) An angle whose measure is less than that of a right angle is acute.
(b) An angle whose measure is greater than that of a right angle is obtuse.
(c) An angle whose measure is the sum of the measure of two right angle is straight.
(d) When the sum of the measures of two angles is that of a right angle, then each one of them is acute.
(e) When the sum of the measures of two angles is that of a straight angle , one of them should be right or obtuse.
8) Find the measure of the angle shown in each figure. (First estimate with your eyes and then find the actual measure with a protractor)
Ans : The measure of the angles shown in above figure are 40˚, 130˚,65˚ and 135˚.
9) Find the angle measure between the hands of the clock in each figure :
Ans : In the first figure , the angle measure is 90˚
In the second figure, the angle measure is 30˚
In the third figure, the angle measure is 180˚
10) Investigate:
In the given figure, protector shows 30˚.Look at the same figure through a magnifying glass. Does the angle becomes larger? Does the size of the angle change?
Ans : The measure of an angle will not change by viewing through a magnifying glass.
11) Measure and classify each angle
| Angle | ∠ AOB | ∠AOC | ∠ BOC | ∠ DOC | ∠DOA | ∠ DOB |
| Measure | 40˚ | 125˚ | 85˚ | 95˚ | 140˚ | 180˚ |
| Type | Acute | Obtuse | Acute | Obtuse | Obtuse | Straight |