I wonder why Sagemath is not able to solve this

var('x a b c')
U_1 = lambda x, a, b, c: c*x*x^1+b*x+a
show(LatexExpr(r'U(x) = '),U_1(x,a,b,c))

# first order x derivative which must be positive

δU_1(x,a,b,c) = diff(U_1(x,a,b,c),x) assume(x>=0) solve_ineq([δU_1(x,a,b,c)>0],[x])