# Solving a linear equation

 1 Hello, I have a problem with the solution of a linear equation given by sage. sage: a,b,c,d=var('a,b,c,d') sage: v(t)=a*t^3+b*t^2+c*t+d sage: v1(t)=diff(v(t),t) sage: g1=v(0)==0 sage: g2=v(5)==1 sage: g3=v1(5)==0 sage: g4=v(1.5)==0.2 sage: solve([g1,g2,g3,g3],[a,b,c,d]) [[a == r1, b == -10*r1 - 1/25, c == 25*r1 + 2/5, d == 0]]  The right solution is a=-62/3675, b=473/3675, c=-16/735, d=0! What's wrong with my implementation in sage? Thomas By the way: How can I realize the typical pre-formatted "sage:... look" in my postings?? asked Aug 29 '11 tmaxara 65 ● 2 ● 4 ● 8 kcrisman 7427 ● 17 ● 76 ● 166 I've edited it to show you how to get that wonderful pre-formatted look - just click "edit" to see how it's done! kcrisman (Aug 29 '11)

 2 Your answer is just one of the ones for this. sage: r1=-62/3675 sage: -10*r1-1/25 473/3675 sage: 25*r1+2/5 -16/735  Maxima returns a solve like this when there is a parameter. In this case, one parameter, r1, which can be any real number. Are you sure your matrix has non-zero determinant? Or did you intend sage: solve([g1,g2,g3,g4],[a,b,c,d])  instead of sage: solve([g1,g2,g3,g3],[a,b,c,d])  Actually, I think this is the real issue - typos trip us all up :( posted Aug 29 '11 kcrisman 7427 ● 17 ● 76 ● 166
 0 Or did you intend sage: solve([g1,g2,g3,g4],[a,b,c,d]) instead of... Yes!! Yesterday I sat an hour ...and now I have made a spelling error! Thank you Thomas posted Aug 30 '11 tmaxara 65 ● 2 ● 4 ● 8

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