Page 29 - Mathematics Class - XI

Viva-Voce

1. What is radian?
Ans. One radian is the measure of an angle subtended at the centre of a circle by an arc of length equal to the
radius of the circle.

2. How p is related to circumference and diameter of a circle?

Ans. p = Circumference of a circle
Diameter of a circle
3. How do you convert radians to degrees?

Ans. To convert radians to degrees, we multiply the radian measure by 180 degrees.
p
π
4. Find the degree measure of the angle    C .
8 

Ans. We know, p radians = 180°

 180 °
\ 1 =  π 
C


 π C  π 180 °
Now,   =  8 × π   = 22.5°

8 


MCQs

1. 1° = ?
a) 1 minute b) 30 minutes c) 60 minutes d) None of these

2. The value of p in degree is
4
a) 45° b) 180° c) 90° d) 360°
3. The value of 60° in radian is
p 5p p p
a) b) c) d)
4 36 3 6

4. What is the radius of that circle in which 22 cm long arc imposes an angle of 36° at its centre.
a) 32 cm b) 22 cm c) 21 cm d) None of these
5. The value of 40°21' into radian is
121p 126p 132p
a) b) c) d) None of these
540 540 560

Answers: 1. c) 60 minutes 2. a) 45° 3. c) p
3
4. d) None of these 5. a) 121p
540
27