In our Week 1 Discussion, we learned that tim sinx = 1 ( assuming that x is measured XOX in radians ). In Section 3.5, page 173, this fact ( along with the addition identity, for the sine function and the fact 8 that lim cos x - 1 = 0 ) is X + 0 X used to prove that the derivative of the sine function is the cosine function: d ( sinx ) = cost dx 1) . use this same methodology ( along with the addition identity for the cosine function ) to prove that the derivative of the cosine function is the negative of the sine function : d( cos x ) - - sinx