Question 1:
What is the measure of (i) a right angle? (ii) a straight angle?
Answer:
(i) The measure of a right angle is 90°.
(ii) The measure of a straight angle is 180°.
Question 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.
Answer:
(a) True
The measure of an acute angle is less than 90°.
(b) False
The measure of an obtuse angle is greater than 90º but less than 180º.
(c) True
The measure of a reflex angle is greater than 180°.
(d) True
The measure of one complete revolution is 360º.
(e) True
Question 3:
Write down the measures of
(a) Some acute angles. (b) Some obtuse angles.
(Give at least two examples of each).
Answer:
(a) 45°, 70°
(b) 105°, 132°
Question 4:
Measure the angles given below using the Protractor and write down the measure.
Answer:
(a) 45º
(b) 120º
(c) 90º
(d) 60º, 90º, and 130º
Question 5:
Which angle has a large measure? First estimate and then measure.
Measure of angle A =
Measure of angle B =
Answer:
Measure of angle A = 40º
Measure of angle B = 68º
∠B has the greater measure than ∠A.
Question 6:
From these two angles which has larger measure? Estimate and then confirm by measuring them.
Answer:
The measures of these angles are 45º and 55º. Therefore, the angle shown in 2^{nd} figure is greater.
Question 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 _______.
(b) An angle whose measure is greater than that of a right angle is _______.
(c) An angle whose measure is the sum of the measures of two right angles is _______.
(d) When the sum of the measures of two angles is that of a right angle, then each one of them is _______.
(e) When the sum of the measures of two angles is that of a straight angle, and if one of them is acute then the other should be _______.
Answer:
(a) Acute angle
(b) Obtuse angle (if the angle is less than 180º)
(c) Straight angle
(d) Acute angle
(e) Obtuse angle
Question 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).
Answer:
The measures of the angles shown in the above figure are 40º, 130º, 65º, 135º respectively.
Question 9:
Find the angle measure between the hands of the clock in each figure:
Answer:
(a) 90°
(b) 30°
(c) 180°
Question 10:
Investigate
In the given figure, the angle measures 30°. Look at the same figure through a magnifying glass. Does the angle become larger? Does the size of the angle change?
Answer:
The measure of this angle will not change.
Question 11:
Measure and classify each angle:
Angle |
Measure |
Type |
∠AOB |
– |
– |
∠AOC |
– |
– |
∠BOC |
– |
– |
∠DOC |
– |
– |
∠DOA |
– |
– |
∠DOB |
– |
– |
Answer:
Angle |
Measure |
Type |
∠AOB |
40º |
Acute |
∠AOC |
125º |
Obtuse |
∠BOC |
85º |
Acute |
∠DOC |
95º |
Obtuse |
∠DOA |
140º |
Obtuse |
∠DOB |
180º |
Straight |