Question

derivative rate question

Answer 1

@zepdrix @amistre64 @Compassionate

Answer 2

well, whats your thoughts so far

Answer 3

i know i have dl/dt which is 1 cm/sec, and im looking for when dA/dt starts to decrease, but i dont get how to find that,

Answer 4

define area, and since we know the perimeter, we can define that as well as a constraint

Answer 5

A= l*w

Answer 6

can we assume that dw/dt is decreasing by 1 cm/sec? im not sure if the perimeter is constant, or just at that point

Answer 7

dont worry about it, we will define w in terms of l from the perimeter setup

Answer 8

so w = 12- L ?

Answer 9

w = 12 - L

w' = L' so yeah, we can do that :) since L' = 1

Answer 10

well, -1

Answer 11

so

w = 12- L
w' = -L'

A = Lw

A' = L'w + Lw'

A' = L'w - LL'

A' = w - L

A' = 12-L- L

Answer 12

when is A' <= 0?

Answer 13

when l = 6?

Answer 14

yep

Answer 15

and thats it, right?

Answer 16

thats it ....

Answer 17

thanks, ive been having lots of rates problems in calc, so its a bit confusing for me.

Answer 18

ive had lots of rate practice over the years :)

Answer 19

good luck