4th derivative

**DINOCALC09** · November 19th 2007, 09:27 AM

If f(x) = (2+3x)^4, then find the 4th derivative of f(x).

A. 0
B. 4!(3)
C. 4!(3^4)
D. 4!(3^5)
E. 4!(2+3x)

**Jhevon** · November 19th 2007, 09:39 AM

Originally Posted by DINOCALC09

If f(x) = (2+3x)^4, then find the 4th derivative of f(x).

A. 0
B. 4!(3)
C. 4!(3^4)
D. 4!(3^5)
E. 4!(2+3x)

C.

think about it, why is that? (you don't have to actually find the fourth derivative explicitly, you can think through it)

**DINOCALC09** · November 19th 2007, 10:00 AM

there are 4 powers so that wil cross out making it 0 which is letter A? correct?

**Jhevon** · November 19th 2007, 01:30 PM

Originally Posted by DINOCALC09

there are 4 powers so that wil cross out making it 0 which is letter A? correct?

no, i told you the answer is C.

**DINOCALC09** · November 19th 2007, 04:58 PM

f(x) = (2+3x)^4

is it something to do with losing the x making it 3^4??

i dont know

**Krizalid** · November 19th 2007, 05:06 PM

Originally Posted by DINOCALC09

If f(x) = (2+3x)^4, then find the 4th derivative of f(x).

A. 0
B. 4!(3)
C. 4!(3^4)
D. 4!(3^5)
E. 4!(2+3x)

$f'(x)=4\cdot3(2+3x)^3.$

So we'll have $4!$ on the final expression and by the chain rule, $3^4,$ can you see that?

Thread: 4th derivative