Math Forum Discussions

Derek Goring

Posts: 3,648
Registered: 12/7/04

Re: how to find x for given y
Posted: Jan 13, 2013 5:14 PM

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On Monday, January 14, 2013 10:14:38 AM UTC+13, johnyyy wrote:
> Hi everyone!
>
> I have a problem with matlab. I was trying to find the answer in the Internet, but I didn't.
>
> dx/dt=sin(x), x(0)=0.5. I have to find time when x=1.5 (t(x=1.5)=?). Can anybody help me, please:)

Sounds like homework, and pretty simple homework at that.
I don't know what you problem with Matlab is, because it really doesn't require Matlab
dx/dt=sin(x)
so, from Abramowitz & Stegun, the integral of cosec(x) is:
t=const + 0.5*log((1-cos(x))/(1+cos(x))
Now, just substitute x=0.5 and evaluate the const for t=0
Then, substitute for x