# Thread: need a bit of help with derivatives...thanks

1. ## need a bit of help with derivatives...thanks

need some help with this one...

2. Originally Posted by mathaction

need some help with this one...
use the product rule: $\frac d{dx} f(x)g(x) = f'(x)g(x) + g'(x)f(x)$

here: $f(x) = t^2 + 4$ and $g(x) = e^t$

3. Originally Posted by Jhevon
use the product rule: $\frac d{dx} f(x)g(x) = f'(x)g(x) + g'(x)f(x)$

here: $f(x) = t^2 + 4$ and $g(x) = e^t$

ok...i came up with this...

e^t*3t^2+e^t*t^3+4

4. Originally Posted by mathaction
ok...i came up with this...

e^t*3t^2+e^t*t^3+4
that's incorrect. try one more time. and use parentheses

5. Originally Posted by mathaction

need some help with this one...
$z'(t) = 3t^2e^t + \left( t^3 + 4 \right)e^t = \left( t^3 + 3t^2 + 4 \right)e^t$

6. oh ok...so its like just combining like terms...

7. Originally Posted by mathaction
oh ok...so its like just combining like terms...
yes, at the end, after i took derivatives