Differential equation f''(x)+\frac{(n-1)(f'(x))^{2}}{\sin h(x)}=0

jubateee

jubateee

Answered question

2022-01-18

Differential equation f(x)+(n1)(f(x))2sinh(x)=0

Answer & Explanation

chumants6g

chumants6g

Beginner2022-01-19Added 33 answers

Let u=f. Then uu2=g and so (1u)=g. Integrate both sides to find u and then integrate once again to find f.
Thomas Nickerson

Thomas Nickerson

Beginner2022-01-20Added 32 answers

To be more explicit (now that some time has passed), this particular equation can be restated as (1u)=(n1)sinh(x),so 1f(x)=(n1)(ln(tanh(x2))+A)
However, Wolfram Alpha indicates that the A=0 case has 1/f'(x) approaching 0 in the limit, which means that f'(x) will not approach 0 for any finite value of A, so it seems like f(x) will never approach a finite limit at infinity (Wolfram Alpha was also not able to find an explicit formula for f(x), even in the A=0 case, so the boundary-value problem is difficult to solve by brute force).
alenahelenash

alenahelenash

Expert2022-01-24Added 556 answers

The general approach would bef(x)+g(x)f(x)2=0f(x)=g(x)f(x)2f(x)f(x)2=g(x)d{1f(x)}=g(x)dx1f(x)=g(x)dx+C0f(x)=(g(x)dx+C0)1f(x)=(g(x)dx+C0)1dx+C1

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