Hi,
f(t) = t Cos w t
f '(t) =
f ''(t) =
Can someone help quick please and tell me how to get the the answers and what rule it is!
thanks
Hi,
Ok here we go:
Your result: $\displaystyle f '(t) = \cos(wt) - wt\sin(wt)$
$\displaystyle
f '(t) = \cos(wt) - wt\sin(wt)=-w(\underbrace{t \cdot \sin(wt)}_{\text{use product rule}}) + \underbrace{\cos(wt)}_{\text{use chain rule}}$
$\displaystyle f''(t)=-w(\sin(wt)+t \cdot (cos(wt) \cdot w)-\sin(wt) \cdot w$
Expand the bracket and collect like terms.