Question 639917
a = 1, b = -11, c = 28
{{{-b/2a = -(-11)/(2(1)) = 11/2}}} 
{{{(4ac - b^2)/(4a) = (4(1)(28) - (-11)^2)/(4(1)) = -9/4}}}
The vertex is (11/2, -9/4).
Here's how to graph:
*[invoke quadratic "x", 1, -11, 28 ]