When $f=0$, each identity $\operatorname{pr}^{(3)}V_i(S)=c_iS$ vanishes on the equation. \b[The equation $S[u]=0$ has all three infinitesimal symmetries $V_1,V_2,V_3$.] They generate the projective transformations of the independent variable.


Solution

Past exam of the mathematics course of the University of Cambridge / 2019 / ii / Paper 3 / 32C / c / i / Solution

 Solution (source code)