1
Let = 1 60 61 + 1 62 63 + + 1 118 119 . Then the value of ( cosec1 )2 is .
Answer
3
Solution
1 a (a+1 )= ((a+1 )-a ) 1 a (a+1 )= a- (a+1 ) 1 .
1 =( 60 + 62 + + 118 )-( 61 + 63 + + 119 ).
Using (180 -a)=- a: the odd terms cancel in pairs (61 with 119 , …, 89 with 91 ); the even terms leave only 60 + 90 = 1 3.
= 1 3 1 cosec1 = 3; square =3
Answer: 3
JEE Advanced 2025 Paper 2