Question 439519
First we bring the function in standard form.{{{y=-2(x^2-2x+1)-2+6}}} or

{{{y=-2(x-1)^2+4}}}. From final function we have:The vertex is:(1, 4) and the 

maximum value is 4. See the graph below.

{{{graph(300, 300, -5, 5, -5, 5, -2(x-1)^2+4)}}}.