I use this code

```
{P1 = RegionPlot[0 <= Cos[y x] <= 1/2, {y, 0, 3}, {x, 0, 5}, 
   PlotStyle -> LightBlue, 
   FrameLabel -> {{Style[Rotate["F", 270 Degree], 15], 
      None}, {Style["y", 15], None}}, BaseStyle -> 15],

 P2 = RegionPlot[0 <= Cos[-y x] <= 1/2, {y, 0, 3}, {x, 0, -5}, 
   PlotStyle -> LightBlue, 
   FrameLabel -> {{Style[Rotate["G", 270 Degree], 15], 
      None}, {Style["y", 15], None}}, BaseStyle -> 15]}

```

and the result is

[![enter image description here](https://i.stack.imgur.com/DnId4.jpg)](https://i.stack.imgur.com/DnId4.jpg)

How can I ask Mathematica to attach the two plots vertically as follows

[![enter image description here](https://i.stack.imgur.com/re0ja.jpg)](https://i.stack.imgur.com/re0ja.jpg)