Question

Given that
f(x) =-2xh(x)
h(5) = -1 and h'(5)=-3
find f'(5)

Answer 1

f(x) = -2x * h(x)
f'(x) = -2x * h'(x) + (-2) * h(x)

Answer 2

f'(5) = -2*5-h'(5) + (-2) * h(5)

Answer 3

f'(5) = -10-(-3)+(-2) *(-1)

Answer 4

f'(5) = -10+3+2=-5

Answer 5

sorry mate that isn't one of the options

Answer 6

not even close :-)

Answer 7

I see my mistake..

Answer 8

sweet, I am more concerned with how to understand this one

Answer 9

-2*5*h'(5) + (-2) * h(5)
f'(5) = -10*(-3)+(-2) *(-1)
f'(5) = 30 + 2 = 32

Answer 10

is that better? haha

Answer 11

f(x) = -2xh(x)
h(5) = -1
h'(5) = -3

f'(x) = -2x[h'(x)] + -2(h(x))
f'(5) = -2(5)(h'(5)) + -2(h(5))
= -10(-3) + -2(-1)
= 30 + 2 = 32

Answer 12

I agree.

Answer 13

I don't know where that - came from haha..

Answer 14

yes, much better. Im going through it to see where I went wrong _ thanks!!

Answer 15

did you use the chain rule?

Answer 16

pls explain if possible would really help

Answer 17

why did you plug in the h's like you did?

Answer 18

okay here we go:
first use the chain rule:
f'(x) = -2x * h'(x) + (-2) * h(x)

Answer 19

Actually that's the product rule. I was wrong about the chain rule earlier.

Answer 20

ok

Answer 21

But what you have written is otherwise correct.

Answer 22

*oh sorry it is.. i never remember the names..haha

Answer 23

can I write the f(x) like this f(x) = (-2x)((h(x)) ?

Answer 24

Certainly.

Answer 25

yea..

Answer 26

then use the product rule..

Answer 27

perfect! now I see the product rule instead of me futzing around with the chain rule.
Thanks a ton!!!

Answer 28

sorry =P

Answer 29

I was doing it loooong before I put the question up - def my fault