Solving a linear equation

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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??