**Understanding Elementary Shapes**

**Exercise 5.4**

*Questions with (*) sign are open-ended questions.*

1). What is the measure of (i) a right angle? (ii) a straight angle?

(i) the measure of a right angle is 90^{0}.

(ii) the measure of a straight angle is 180^{0}.

2). Say True or False:

a). The measure of an acute angle < 90^{0}.

b). The measure of an obtuse angle < 90^{0}.

c). The measure of reflex angle > 180^{0}.

d). The measure of one complete revolution = 360^{0}.

e). If m∠A = 53° and m∠B = 35°, then m∠A > m∠B^{ 0}.

Answers:

a). The measure of an acute angle < 90^{0}.

True.

b). The measure of an obtuse angle < 90^{0}.

False.

c). The measure of reflex angle > 180^{0}.

True.

d). The measure of one complete revolution = 360^{0}.

True.

e). If m∠A = 53° and m∠B = 35°, then m∠A > m∠B^{ 0}.

True.

3). Write down the measure of

a). some acute angles.

1^{0}, 30^{0}, 35^{0}, 45^{0}, 78^{0} are measures of some acute angles.

b). some obtuse angles.

(give at least two examples).

91^{0}, 130^{0}, 105^{0}, 145^{0}, 178^{0} are measures of some obtuse angles.

4). Measure the angles given below using the Protractor and write down the measure.

Answer:

5). Which angle has a large measure?

First estimate and then measure.

Measure of Angle A = 40°

Measure of Angle B = 50°

Angle B has a large measure.

6). From these two angles which has larger measure? Estimate and then confirm by measuring them.

Answer:

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 measures of two right angles is __straight angle__.

d). When the sum of the measure 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 and if one of them is acute then the other should be __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).

Answer:

9). Find the angle measure between the hands of the clock in each figure:

9.00 a.m. 1.00 p.m. 6.00 p.m.

Answer:

10). Investigate

In the given figure, the angle measure 30^{0}. Look at the same figure through a magnifying glass. Does the angle becomes larger? Does the size of the angle change?

Answer:

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