The question for session4 requires you to find the derivative of sin(2x). i tried using various sin/cos properties but nothing was able to cancel out the deltax in the denominator. i tried things like sin(x+y) = sin(x)cos(y)+cos(x)sin(y), and cos(x+y) = cos(x)cos(y)-sin(x)sin(y), and sin(x)^2 = 1 - cos(x)^2.