We talked about the derivatives of common trigonometric functions. The only ones you really need to know are those of sin and cos (well, actually they all follow from knowing the value of sin(x)/x as x goes to zero), then the rest can easily be derived from those.
The limit of sin (x)/x as x goes to zero is very important. In a sense, it tells us that sin(x) is close to x when x is close to zero. We discussed how to compute various related limits, like sin(6x)/x, and sin(6x) / sin(2x), as x goes to zero. They all used the "multiplying by one" trick which is a very useful one to remember.
We worked through Section 3.3.5, 13, 25, 39, 41 and 3.4.31,39 .