Page 155 - Math Skill - 5

Geometry 153

5. Measure each of the following angles and classify them as acute, obtuse or right angle.

(a) (b) A (c) R
I

B
G H C S T
6. Classify each of the following angles as acute, obtuse, right or reflex angle.
(a) 86° (b) 43.5° (c) 90.7° (d) 128° (e) 273° (f) 90°

Drawing Angle Using a Protractor
C
Let’s draw an angle of 80° using ruler and protractor.

Step 1: Draw a ray AB .

Step 2: Place the protractor in such a way that its centre
lies on A and its horizontal edge lies along AB.
Step 3: Look carefully along the scale whose 0° mark lies
on AB until you reach 80° mark on the rim. A B
Step 4: On that mark, put a dot with a fine pencil and name it as C.

Step 5: Remove the protractor and draw ray AC using a ruler.

Thus, ∠CAB = 80°.

Pairs of Angles

Complementary Angles P A

Two angles are said to be complementary, if the sum
of their measures is 90°. For example, 65° and 25° are 25°
pair of complementary angles or ∠PQR and ∠ABC are Q 65° B C
complements of each other. R

X G Supplementary Angles
Two angles are said to be supplementary, if the sum of
120° 60° their measures is 180°. For example, 120° and 60° are pair
Z Y H I of supplementary angles. Thus, ∠XYZ and ∠GHI are
supplements of each other.

Let’s Attempt

Example 1: Find the complement of 43°. Example 2: Find the supplement of 84°.
Solution: Complement of 43° = (90° – 43°) Solution: Supplement of 84° = 180° – 84°
= 96°
= 47° Thus, the supplement of 84°

Thus, the complement of 43° is 47°. is 96°.