# unsolved equation Dear sage user,

Could you help me to find z = z(t)?, if:

((2.867e28) / (sqrt (r^3 - (2.1e13)^3 )) ) == (( (2.121e8)*(sqrt(2*(z^2) -1))) / ( z - sqrt (z^2 - 1)))


with,

r == ((1.97774e13)*(sqrt(sqrt(t)))) + ((3.55214e12)*(sqrt(t)))

1 < t < 6000

z(t= 1) = 100

r (t= 1) = 2.332954e13


thanks!!

I couldn't solve it!!!

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This isn't a system of linear equations, nor a system of ordinary differential equations, unless you've made a typo. Try rephrasing your question, or looking at the Sage documentation about solving linear or differential equations.

could you tell me,what kind of equation do you think is it?. I found this equation from physical principles of shock wave to describe the temporal evolution of relativistic blastwaves. z is the lorentz factor ( http://en.wikipedia.org/wiki/Lorentz_factor ) and r is the shock radius. Thank you for your comment!

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A differential equation would involve the derivative z'(t) which you don't have in your equation(s).

If you substitute the value of r into the first equation you would have a single non-linear equation relating z and t. You may be able to solve this equation using the solve command. You don't have any unknown parameters in the expression for r or the equation involving z so you might not be able to solve the equation and have the values at t=1 that you specify be true.

You might try something like:

r,z,t = var('r,z,t')
equation = ((2.867e28) / (sqrt (r^3 - (2.1e13)^3 )) ) == (( (2.121e8)*(sqrt(2*(z^2) -1))) / ( z - sqrt (z^2 - 1)))
equation = equation.subs(r == ((1.97774e13)*(sqrt(sqrt(t)))) + ((3.55214e12)*(sqrt(t))))
solve(equation, t)


When I tried this I got:

Is  (2*z^2-1)*(z-sqrt(z^2-1))  positive, negative, or zero?


meaning that Maxima (the solver underneath Sage) can't solve the equation without more information.

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Thank you very much for your kind attention and your suggestions. However I need to find z as a function of t, when t vary 1 - 1000 with step of 10. is it possible to do that?