if the function f(x) = x^(3)+3(a-7)x^(2)+3(a^(2)-9)x -1 has a positive point of maximum, thena belongs to what values in Real numbers

df(x)/dx = 3x^2 +6(a-7)x +3(a^2 -9)=0, solving the quadratic equation in x and then simplifying, we get

x= 7-a±√(58-14a) thus firstly 58>14a,a<29/7 , d²f(x)/dx²= 6x+6(a-7)<0,7-a>x, 7-a>x±√(58-14a), 7-a=x+√(58-14a),

x=7-a-√(58-14a)>0 implies a²>9. Also, we have the earlier result a<29/7, therefore a<-3 or +3<a<29/7