Velocity from displacement

Hi the question is as following,
The displacement of a body after time t is given as s = tsint + cost. Calculate its velocity and acceleration values at t = 3
(an: -2.970; -1.413)

I used equation ds/dt = v to find the derivative which is
v = tcost + sint -sint
but when i put t = 3 to the equation can't get the right answer, I thought it would be the problem of the derivation but I can't find which goes wrong.
(Crying)

Quote:

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Originally Posted by yanmingfu

Hi the question is as following,
The displacement of a body after time t is given as s = tsint + cost. Calculate its velocity and acceleration values at t = 3
(an: -2.970; -1.413)

I used equation ds/dt = v to find the derivative which is
v = tcost + sint -sint
but when i put t = 3 to the equation can't get the right answer, I thought it would be the problem of the derivation but I can't find which goes wrong.
(Crying)

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Your derivative is correct so your mistake lies elsewhere.

oh, I just found where goes wrong, when I put t = 3 in equation I forgot to change it the the degree 3 = 171.88 degree(Nod) thanks anyway.(Happy)