So let's say you have like a pendulum but instead of the one string you have two strings attached to two fixed supports (I tried to include a picture). Let's say you pull it back and swing it so that it is swinging in and out of the screen. Would its period of oscillation be the same as if there were one string of length equal to the vertical height that the supports are above the pendulum? I tried going after this with forces but it isn't even easy to draw. All I can think is that in the limiting case when the "d" goes to zero it's a simple pendulum again. Any ideas?