Mimicking the investigation we performed to get an idea for the derivative for e^x, we'll use desmos to reveal a startling relationship between sine and cosine. Duration: 7:30

Combining the utility of the Sum Formula for sine and a few special trig limits, we prove that the derivative of sin(x) is cos(x) using the limit definition. So that's why we had to write those two obscure limits on our memory card. Duration: 7:06

Now it's your turn. Use the limit definition of the derivative to show that the derivative of cos (x) is -sin (x). As the previous video demonstrated, you will need the Sum Formula for cosine and our two special trig limits. One of you lucky scholars will get to present your proof in class for Experience Points.

Now let's put our two new derivative rules into practice on a few examples. Duration: 7:32