Answer:
<h3>
7 cm</h3>
Step-by-step explanation:
For any quadratic function f(x)=ax²+bx+c given in form f(x)=a(x-h)²+k, where:
h=-b/2a and k=f(h) the point (h, k) is vertex of the function graph.
It means that k is maximum (if a<0) or minimum (if a>0) value of function and x=h is the x which will maximize function.
A(x) = x(28-2x) = 28x - 2x² = - 2x² + 28x ⇒ a = -2 , b = 28
h = -28/[2•(-2)] = 7
