JEE Main202228 Jun 2022Evening ShiftMathematicsInverse Trigonometric FunctionsActual
The value of lim n → ∞ 6 tan ∑ r = 1 n tan - 1 1 r 2 + 3 r + 3 is equal to
Options
- A1
- B2
- C3
- D6
Correct answer
C. 3
Step-by-step solution
Let S = ∑ r = 1 n tan - 1 1 r 2 + 3 r + 3 So, T r = tan - 1 1 r 2 + 3 r + 2 + 1 = tan - 1 ( r + 2 ) - ( r + 1 ) 1 + ( r + 1 ) ( r + 2 ) = tan - 1 r + 2 - tan - 1 r + 1 T 1 = tan - 1 3 - tan - 1 2 T 2 = tan - 1 4 - tan - 1 3 . . T n = tan - 1 n + 2 - tan - 1 n + 1 ⇒ ∑ r = 1 n tan - 1 1 r 2 + 3 r + 3 = tan - 1 n + 2 - tan - 1 2 i.e. 6 tan lim n → ∞ ∑ r = 1 n tan - 1 1 r 2 + 3 r + 3 = 6 tan lim n → ∞ ∑ r = 1 n tan - 1 n + 2 - tan - 1 2 = 6 tan π 2 - tan - 1 2