How do you know if the parabola is stretched or shrunk?

stretched or shrunk has to do with the variable at the beginning of the equation. In this case .5, since the value is smaller than 1 it is stretched, if it were larger than 1 it would be shrunk. This is because the .5 makes the values increase (or decrease since it is negative) at a slower rate, a value higher than 1 makes it increase or decrease at a faster rate.