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How to get positive solution only of a quadratic equation

asked 2013-01-21 14:25:37 -0500

Majid Khonji gravatar image

I have a quadratic equation when I give it to the solver, I get two solutions, one positive one negative. By doing this: solve(eq, x)[0]

we can select which one. However, I want to insure that is always positive. I don't want manual stuff!

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answered 2013-02-22 13:05:57 -0500

lftabera gravatar image


sage: solve([x^2+2*x-3==0, x>=0],x)
[[x == 1]]
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answered 2013-01-21 14:41:41 -0500

kcrisman gravatar image
sage: eq = x^2+2*x-3==0
sage: solve(eq,x)
[x == -3, x == 1]
sage: [sol for sol in solve(eq,x) if sol.rhs()>0]
[x == 1]

But keep in mind that not every quadratic equation has one positive and one negative solution! (Or even two real solutions...)

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Asked: 2013-01-21 14:25:37 -0500

Seen: 3,197 times

Last updated: Feb 22 '13