First Order Differential Equations where a<x<b (Intial value?)

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SUMMARY

The discussion focuses on solving the first-order differential equation given by the expression sqrt(y-x^2y)*dy/dx = -xy, specifically within the interval -1 < x < 1. The solution provided is y = 1/4(2C*sqrt(1-x^2) + C^2 - x^2 + 1), where C is a constant. The participants clarify that the inequality indicates the domain of x for which the solution is valid, and that outside this range, the solution may involve different mathematical functions, such as inverse trigonometric functions.

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  • Familiarity with solving differential equations involving inequalities
  • Knowledge of square root functions and their domains
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kafuzz
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Hi, I'm having trouble understanding what to do when a First order equation has an inequality at the end of it.

For example : sqrt(y-x^2y)*dy/dx = -xy where -1<x<1

I've solved the differential equation with y = 1/4(2C*sqrt(1-x^2) + C^2 -x^2 +1) where C is a constant.

What do I do with the inequality? Is it an initial value problem?
 
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welcome to pf!

hi kafuzz! welcome to pf! :smile:
kafuzz said:
HI've solved the differential equation with y = 1/4(2C*sqrt(1-x^2) + C^2 -x^2 +1) where C is a constant.

your solution contains √(1 - x2) …

you'll probably find that if |x| > 1, you get a solution with √(x2 - 1), or maybe some inverse trig function :wink:
 

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