Please suggest a substitution for solving or any method of

Donald Johnson

Donald Johnson

Answered question

2021-12-08

Please suggest a substitution for solving or any method of solving:
y(x)cot(y(x))=y(x)2+c

Answer & Explanation

esfloravaou

esfloravaou

Beginner2021-12-09Added 43 answers

Substituting u=sin(y) one gets
u=(sin(y))=(cos(y)y)=cos(y)ysin(y)y2=csin(y)=cu
which is, depending on the sign of c, an oscillation equation or an exponential function which is easily solvable for u and thus for y.
u={a1cos(|c|x)+a2sin(|c|x)for c<0b1+b2xfor c=0c1ecx+c2ecxfor c>0
Serita Dewitt

Serita Dewitt

Beginner2021-12-10Added 41 answers

cotyy=y2+c
Substitute y=py=pdpdy
ppcoty=p2+c
2pp2+cdp=2tan(y)dy
ln|p2+c|=2ln|cos(y)|+K1
p2=K1cos2(y)c
y=K1cos2(y)c
dyK1cos2(y)c=x+K2
with u=sin(y)
duK1+cu2=x+K2

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