# I'm stuck with dis problem....

• December 18th 2008, 09:02 PM
calculus-geeks09
I'm stuck with dis problem....
ok i know how to do this problem but I'm stuck at the last part.

the problem is :

$f(t)=sqrt(4t+1)$

find $f''(2)$

I found the 1st derivative but i'm stuck at the 2nd derivative! I know that once I find the 2nd F''(x) I will plug the 2 but I'm stuck at the 2nd derivative.

Plz help me get the 2nd derivative and i'm set !!!!

Thanks
• December 18th 2008, 09:03 PM
Jhevon
Quote:

Originally Posted by calculus-geeks09
ok i know how to do this problem but I'm stuck at the last part.

the problem is :

$f(t)=sqrt(4t+1)$

find $f''(2)$

I found the 1st derivative but i'm stuck at the 2nd derivative! I know that once I find the 2nd F''(x) I will plug the 2 but I'm stuck at the 2nd derivative.

Plz help me get the 2nd derivative and i'm set !!!!

Thanks

what did you find for the first derivative?
• December 18th 2008, 09:08 PM
calculus-geeks09
this is the 1st derivative

$2t(4t+1)^-1/2$

or this is similar to :

$2t/sqrt.(4t+1)$
• December 18th 2008, 09:11 PM
Jhevon
Quote:

Originally Posted by calculus-geeks09
this is the 1st derivative

$2t(4t+1)^-1/2$

or this is similar to :

$2t/sqrt.(4t+1)$

both are incorrect.

the first derivative is $2(4t + 1)^{-1/2}$

now can you find the second?

by the way, to differentiate the expressions you had, you would use product rule in the first case and quotient rule in the second. but neither of those are needed for the correct answer
• December 18th 2008, 09:14 PM
calculus-geeks09
Quote:

Originally Posted by Jhevon
both are incorrect.

the first derivative is $2(4t + 1)^{-1/2}$

now can you find the second?

lol ! 1 little mistake changed my whole answer ! Thanks

Thanks I got it !!!!

thanks so much, u are a life saver !