This is why they shouldn't hand out engineering degrees online.
Obviously without the middle ladder the long ladder would push down to the guttering and the top one would either slide backwards if tied at the top or drop forwards and slide off the roof.
Not that this was really worth a debate, but I feel compelled to call out retardation when it's so evident.
How/is it attached was the question, retard, not "how do lateral forces work?" I literally said that in the single sentence you quoted:
"...unless it's supporting (tied to?) the long one perpendicularly." What part of the house is in the perpendicular direction of the ladder? What is a perpendicular force? Derr.
Your response almost completely mirrors what I said, only you point out the fact that the gutter would get crushed by the ladder, as if that was even a question in the first place. Worse is that you failed to answer the question in the first place. You might as well show us how intelligent you are by explaining how we have to use ladders because of gravity. If you were my student, I'd fail you for lack of reading comprehension alone.
If you look at the picture, the perpendicular ladder's outer dimensions are thinner than the long ladder's inner dimensions. It
appears as if it's just leaning there on one of the rungs of the long ladder. There is no rope visibly fastened like the top and long ladder have. I don't see any hooks or ledges for it to rest on it.
In summary, you're a retard. You're welcome.