I have the planes:

Plane 1: x + 3y - 5z = 0
Plane 2: x + 4y - 8z = 0
Plane 3: - 2x - 7y + 13z = 0

and I want to plot them in a 3d space with plot3d.

I tried to assign each plane to its own variable like this:

P1 := x+3y:
P2 := x+4y:
P3 := -2x-7y:
plot3d([PlaneOne, PlaneTwo, PlaneThree], x = -8 .. 8, y = -20 .. 20, plotlist = true, color = [blue, red, green])

The planes plot, but they aren't showing correctly.

Here's how they should look, and here's how they look.

Please help. I don't know what I'm doing wrong