Question 804870
vertex form is
{{{y=a(x-h)^2+k}}}}
To get it into vertex form, complete the square.
{{{y=-x^2+4x+4}}}
{{{y=-(x^2-4x-4)}}}
{{{y=-(x^2-4x+4-4-4)}}}
{{{y=-(x-2)^2+8}}}