This is a downward facing parabola, so its range comes in the form
where m is the y coordinate of the vertex of the parabola.
We can find the x coordinate of the vertex using
![x=-(b)/(2a)=-(-2)/(-2)=-1](https://img.qammunity.org/2020/formulas/mathematics/middle-school/47iu61vau3dqcgr5rlg9mq15yacmzub3ml.png)
And if we plug -1 in the equation we get the y coordinate of the vertex:
![y=-(-1)^2-2(-1)+3 = -1+2+3=4](https://img.qammunity.org/2020/formulas/mathematics/middle-school/olliw72jqfho0va17j05rgvyqkniy9odsq.png)
So, the range is the interval
![(-\infty, 4)](https://img.qammunity.org/2020/formulas/mathematics/middle-school/z8orxntm5zx4y4rxwvih99ubp6w8y97b30.png)