In a circle of radius 21 cm, an arc subtends an angle of 60° at

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Fig. 12.3
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In a circle of radius 21 cm, an arc subtends an angle of 60° at the centre. Find :

(i)    the length of the arc
(ii)    area of the sector formed by the arc
(iii)    area of the segment formed by the corresponding chord.


Here, we have
r = 21 cm and ө = 60°
Let OACBO is the given sector and ACB with overbrace on top is the length of arc, then,



Here, we haver = 21 cm and ө = 60°Let OACBO is the given sector and
(i) The length of the arc open parentheses ACB with overbrace on top close parentheses

equals 2 πr cross times straight theta over 360
equals space open parentheses 2 cross times 22 over 7 cross times 21 cross times fraction numerator 60 over denominator 360 degree end fraction close parentheses space cm squared
equals space 22 space cm squared

(ii) Area of the sector formed by the arc (OACBO) 

equals 2 πr cross times straight theta over 360
equals space open parentheses 2 cross times 21 cross times 21 cross times fraction numerator 60 over denominator 360 degree end fraction close parentheses space cm squared
equals space 231 space cm squared

(iii) Area of Minor segment (ACBA)

= Area of sector (OACBO) - Area of triangle (OAB)

equals space πr squared cross times space straight theta over 360 minus 1 half straight r squared space sin space straight theta
equals space 231 minus 1 half straight x space space 21 space straight x space 21 space straight x space sin space 60 degree
equals open parentheses 231 minus 1 half straight x space space 21 space straight x space 21 space straight x space fraction numerator square root of 3 over denominator 2 end fraction close parentheses space cm squared
equals space open parentheses 231 minus fraction numerator 441 square root of 3 over denominator 4 end fraction close parentheses space cm squared.

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