How to get positive solution only of a quadratic equation

Majid Khonji
11 ●1 ●1 ●2

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!

2 Answers

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kcrisman
12242 ●42 ●136 ●255

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...)

lftabera
171 ●4 ●6

Also

sage: solve([x^2+2*x-3==0, x>=0],x)
[[x == 1]]

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Asked: 2013-01-21 21:25:37 +0100

Seen: 7,148 times

Last updated: Feb 22 '13