Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

The ODE is $dr/d(\theta)$ = $r^2/\theta,$ $r(1) = 2$
separable equation and integrate both sides: $\int(dr/r^2$ - $\int d\theta/\theta$ =$0$
-$\frac{1}{r} - ln(\theta) = c$

solve for c: $-\frac{1}{2} - ln(1) = c$
-$\frac{1}{2}$ = c

plug back into equation: -$\frac{1}{r} - ln(\theta) = -\frac{1}{2}$

solve for r:
$r = \frac{2}{1-2ln(\theta)}$

My quetion is, how do I find the interval for the solution?

share|cite|improve this question
maybe you wanted to type $\ln(1)=0$ – Evgeny Savinov Feb 5 '12 at 21:32

Hint: you need $\ln(\theta)$ to be defined, and you also can't let the denominator be $0$.

share|cite|improve this answer

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.