In the episode after Cell absorbs 17, Tien will jump in. After being called a "no-count" by Cell, he makes a triangle with his hands and does an attack called "Tribeam." However, it makes a perfectly rectangular hole in the ground!
So? When Gokou uses Kamehameha he folds his hands in a bowl-like shape, does that mean the Kamehameha is bowl-shaped as well? The fact that Tenshinhan makes a triangle with his hands doesn't have to mean that the beam has to be triangular as well. It's just how the attack is powered up. And the actual name is "Shin Kikoho" (wich is an improved version of the original Kikoho). The name "Tribeam" is just another one of FUNi's crappy excuses for attack names ("Special Beam Cannon", "Destructo Disc").
Actually Piccolo.........I know this guy that works for FUNimation and they said that after they had released that episode they re-looked at it to make sure everything was ok and they found out that that was a mistake but they couldn't do any thing about it cause it had already been showed!
Actually, his 'tribeam' attack hits and destroys a zone he wants to. The first time he used it, back in Dragon Ball, he pointed it at a specific zone, the ring where he was fighting Goku, which was a square.
The triangle he made with his hands was probably only used for targeting purposes. As I remember it he zoomed in on Cell while looking through the triangle.