I know second derivative of sin cos sinh cosh functions are equivalent themselves with different sign. so my question is there any function similar or not? Any help might be appreciated.

  • $\begingroup$ This is an off-topic. First it is on mathematics, rather than MMa, second it is based on a rough mathematical error. $\endgroup$ Apr 28, 2017 at 13:49
  • $\begingroup$ thanks but what's your suggested site to ask my question?? $\endgroup$
    – Farid
    Apr 28, 2017 at 13:51
  • $\begingroup$ It is Stack Exchange Mathematics $\endgroup$ Apr 28, 2017 at 13:53
  • $\begingroup$ Your question may be put on-hold or migrated as it seems to be off-topic, i.e it is not about Wolfram Mathematica programming. Don't be discouraged by that cleaning-up policy. Your future good questions are welcome. Learn about common pitfalls here. You can still edit your question to revert this decision. $\endgroup$
    – rhermans
    Apr 28, 2017 at 14:29

1 Answer 1

DSolve[x''[t] == -x[t], x[t], t]
{{x[t] -> C[1] Cos[t] + C[2] Sin[t]}}

So C[1] Cos[t] + C[2] Sin[t] for any complex C[1] , C[2] and t.

  • 1
    $\begingroup$ Also for complex t ;-) $\endgroup$
    – LLlAMnYP
    Apr 28, 2017 at 14:50

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