So there are: (1) the opening direction is upward, the symmetry axis is x= 1/2, and the vertex coordinates are (1/2, m- 1/4).

(2) When m> 1/4, the vertex is above the X axis;

When m= 1/4, the vertex is above the X axis;

When m< is at 1/4, the vertex is below the X axis.

2. Solution: According to the meaning of the question, the parabolic equation y=- 1/4x? +4 Construct a coordinate system and put the rectangle into the coordinate system, then the coordinates of the four vertices in a square are (-4, -2), (4, -2), (-4, 0) and (4, 0) respectively.

(1) When the tunnel is a one-way street, the truck can travel in the middle of the tunnel, and the positions of the vertices on both sides of the truck in the coordinate system are (-1, 2) and (1, 2) respectively.

When x=- 1 and 1, the corresponding coordinates on the parabola are (-1, 4- 1/4) and (1, 4- 1/4) respectively.

The height corresponding to the change point is: 2+(4- 1/4)=5.75(m).

That is, they are all higher than 4m and can pass through the tunnel.

(2) If there is a two-way lane in the tunnel, the truck runs on the central axis, which is 6m outside the tunnel. On the other side, the coordinate value of X axis is 2, and the corresponding parabola ordinate value y=4-( 1/4)*2? =3, that is, the tunnel height here is (2+3) m = 5m > 4m

Explain that trucks can still pass through the tunnel at this time.