Select the x cooridinate of the vertex of the parabola defined by the function f(x)=-5+9x+1?

select the x cooridinate of the vertex of the parabola defined by the function f(x)=-5+9x+1

Well,
i suppose it' s f(x) = -5x^2 + 9x + 1
so, one practical technique of finfing the vertex's first coordinate is :
f has one single maximum (in this case) :
-----> the only point for which the tangent is horizontal, so
slope = derivative at this point
therefore, as
f(x) = -10x + 9
the max is reached for : ---> x = 9/10

hope it'll help !!