The calculation is correct and this solution would work, IF and only IF the bridge was really thin. But, unless the people are tightrope walkers, you would probably assume the bridge is maybe a half meter thick. If that is the case, then you would have to move the angled bridge (the first one) half a meter in towards the corner. Otherwise, you would not be able to secure both sides of the width on the land. And if you don't secure the two ends, then it won't support the the second bridge. Also, if both sides of the width aren't secured, then the bridge wont stay flat, and you wouldn't be able to walk on it anyway. Unless we are dealing with an army of tightrope walkers.
It wouldn't matter how thin the bridge is. The left edge will ALWAYS be 9.5m. If it were a thin bridge, it will STILL be 9.5m. Thus, it can span the same distance as the thin bridge with the right side also resting firmly on dry ground.