Thread: Problems deriving trig functions

1. Problems deriving trig functions

Hi,

I'm given two trig functions I need to find the derivative of:

y = c*cost + t^2sint

y= tsint/(1+t)

For the first function, I try applying the product rule and get 1(cost)+c(-sint) + 2t(sint) + t^2(cost). The problem is that that is wrong, and the actual answer is c(-sint) + 2t(sint)+t^2(cos). I'm not sure why one of the terms get cancelled out though?

For the second function, I try applying the quotient rule. I end up with ((1(sint)+t(cos))(1+t) = t(sint)(1))/(1+t)^2. The problem is that the answer is actually ((cost)(1+t)-t(sint)(1))/(1+t). Again, the first term cancels for reasons unknown. Could anyone help shed some light on this one?

Thanks!