The following solve()
resists to any argument (to_poly_solve... calling giac sympy or anything else) in the way that it return an implicit solution in y
var('y')
A=n((1/2)*((1/4)*log(35000*0.25+100)+(3/4)*log(100)))
B=n((1/2)*((1/2)*log(35000*0.25+100)+(1/2)*log(100)))
C=(1/2)*A+ (1/2)*B
D=(1/2)*((1/2)*log(35000*0.25+100-y)+(1/2)*log(100-y))
sol=solve(D-C==0,y)[0]
sol
Of course I can find the solution acting the following way, but I find it after a long search and it seems inelegant. Is there an other way ?