Question

I am supposed to graph this

y= -x^2+2x

he told us to coplete the square to get us the vertex, but how do i complete the square with a - in front of the x^2??

Answer 1

This way:
-x^2 + 2 x = y

x^2 - 2 x = -y

x^2 - 2 x + 1 = -y+1

(x-1)^2 = -(y-1)

vertex at (1,1)
negative sign means opens down (sheds water)