Question 1071424
Factorization should be enough for this one.


{{{f(x)=x^2-4x=x(x-4)}}}


Roots are  0 and 4, so you know symmetry axis is at x=2 (because in the exact middle of the roots) and the vertex will occur also for x=2.  You find that value!


{{{graph(300,300,-5,5,-5,5,x^2-4x)}}}