About differential equations. 1. While solving differential equations, is it okay to find an expression containing y and x (without y′) from which it's rather difficult to express y, for example, (ln^2(y))/(y)-x/y=C?

Gauge Odom

Gauge Odom

Answered question

2022-09-16

About differential equations.
1. While solving differential equations, is it okay to find an expression containing y and x (without y′) from which it's rather difficult to express y, for example,
ln 2 ( y ) y x y = C ?
2. Does it make sense to try to find x(y) in some problems where it's easier?

Answer & Explanation

gasskadeu7

gasskadeu7

Beginner2022-09-17Added 21 answers

Step 1
1) Yes, it is typical to find the solution in a manner where y and x are implicitly defined.
Step 2
2) Yes, in some cases it is easier to express x = f ( y ) instead of y = g ( x ).
tamola7f

tamola7f

Beginner2022-09-18Added 2 answers

Step 1
For instance, in the case of a separable equation such as g(y)dy=f(x)dx, you are lucky if both members can be integrated analytically.
Step 2
Then you obtain a form like
G ( y ) = F ( x ) + c
and you are even more lucky if G is invertible analytically. It can arise that G is not monotonic, and the solution must be split in several branches.

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