Question 694390
graph 
y= 1/2(x-1)(x+2)
y=(1/2)(x^2+x-2)
complete the square:
y=(1/2)(x^2+x+1/4)-1-1/8
y=(1/2)(x+1/2)^2-9/8

This is an equation of a parabola that opens upwards.
Its standard form of equation:y=A(x-h)^2+k, (h,k)=(x,y) coordinates of the vertex
for given equation:y=(1/2)(x+1/2)^2-9/8
vertex: (-1/2,-9/8)
see graph below:
{{{ graph( 300, 300, -10,10, -10, 10,(1/2)(x+.5)^2-9/8) }}}