- #1

Physics lover

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- Homework Statement
- Problem -: lim cos(pi(n^2+n)^(1/2)) where n tends to infinity.

- Relevant Equations
- Costheta=cottheta/cosectheta

L'Hospital rule

I wrote cos(pi(n^2+n)^(1/2)) as cot(pi(n^2+n)^(1/2))/cosec(pi(n^2+n)^(1/2)) and as we know cot(npi)=infinity and cosec(npi)=infinity , so i applied L'Hospital.After i differentiated i again got the same form but this time cosec/cot which is again infinity/infinity.But if i differentiate it i will get the same form again.So what to do now.