First order non linear differential equation , non separable First time I run into an equation of this "form", for non linear equations I know separation of variables and substitution. It doesn't seem to be homogenous of degree 0 so the substitution v=x/t is out of the question? Applying ln to both sides didn't do much either x′(t)=e^(t+x(t))−1,x(0)=1 Wolfram gives the solution x(t)=−ln(c_\1−t)−t

Messiah Sutton

Messiah Sutton

Answered question

2022-11-15

First order non linear differential equation , non separable
First time I run into an equation of this "form", for non linear equations I know separation of variables and substitution. It doesn't seem to be homogenous of degree 0 so the substitution v = x t is out of the question? Applying ln to both sides didn't do much either
x ( t ) = e t + x ( t ) 1 , x ( 0 ) = 1
Wolfram gives the solution
x ( t ) = ln ( c 1 t ) t

Answer & Explanation

avuglantsaew

avuglantsaew

Beginner2022-11-16Added 15 answers

One can substitute v ( t ) = t + x ( t ), which results in v ( t ) = 1 + x ( t ) by differentiating both sides with respect to t. Hence, we have:
x ( t ) = e t + x ( t ) 1 v ( t ) 1 = e v ( t ) 1 v ( t ) = e v ( t )
This ODE is separable, and you know how to solve such.
Madison Costa

Madison Costa

Beginner2022-11-17Added 3 answers

Read
x ( t ) + 1 = ( x ( t ) + t ) = e x ( t ) + t
and immediately
e x ( t ) + t = C t .

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