Bit of help please chaps:

Finding the vertex of a Parabola, two methods, graph and formula.

Formula: $\displaystyle h= -5h^2 + 10t$

Now when i've graphed it, it comes out positive in terms of co-ordinates, however when you apply the formula:

Letting a= -5, b= 10, c= 0

$\displaystyle ( - \frac{b}{2a} , C - \frac{b^2}{4a}) $

For X Co-Ord

$\displaystyle ( - \frac{10}{2 x ^-5} ) = -1$

For Y Co-Ord

$\displaystyle 0 - \frac{10^2}{4 x -5}) = -5$

The vertex of the parabola on the graph shows X = 1 and Y = 5 so how or why am i getting the negatives?!

Thanks