Find the vertex: -1/4x^2+9/5x+2

Answer 1

I assume you mean:
-x^2/4 + 9 x/5 + 2 = y
complete the square
first multiply by -4
x^2 - 36 x/5 - 8 = y

x^2 - 36 x/5 = y+8

x^2 - 36 x/5 + (18/5)^2 = y + 8 + 12.96

(x-18/5)^2 = y + 20.96
so vertex at
( 3.6 , -20.96)