Calculus

You dont need infinities and calculus to do 3D graphics and video games.

Here is why:
http://www.youtube.com/watch?v=Oe2DZc6BXZk

that is, all the trigonometry you learned at school was a waste of your time, as it could be replaced with linear algebra.

Okay, so you're making a tower defense game. You have an invader moving down the line and a tower shooting at him. The tower shoots a bullet. Using linear algebra, you can calculate where the invader will be in the time that it will take the bullet to get there, and move the bullet towards that point in the same time. BOOM. You're stuck. First of all, how much of the bullet's velocity is x, and how much is y? Second, to what angle do you rotate the bullet? That's trig. Really, really simple trig.