Let y=2x2.
Find the change in y, delta y when x=4 and delta x=03

Question

Let y=2x2.
Find the change in y, delta y when x=4 and delta x=03

hartnn · Answer

$\large \Delta y=4x\Delta x$
just plug in values!

anonymous · Answer

how did you get that?

hartnn · Answer

can you differentiate y=2x^2 ?

anonymous · Answer

yes 4x

hartnn · Answer

thats dy/dx = 4x
dy = 4x dx

anonymous · Answer

I see.

anonymous · Answer

I plug numbers into the equation and got an answer but the online homework says its wrong

hartnn · Answer

x=.. ? 
3? 
why u wrote 03 ?

anonymous · Answer

0.3

anonymous · Answer

sorry about that

hartnn · Answer

delta y = 4*4*0.3 = 16*0.3 =4.8

anonymous · Answer

I got 4.8 as well but it told me that it was wrong

hartnn · Answer

screenshot ?

anonymous · Answer

sorry dont have a camera right now

anonymous · Answer

wish i had

hartnn · Answer

there must be a PrtSc key in your keyboard ?

anonymous · Answer

whats that

hartnn · Answer

it captures screenshot.
that you can paste in Paint and save it

anonymous · Answer

No i cannot find it! but i found print screen bottom

hartnn · Answer

good...press it and use paint...

anonymous · Answer

ok, i pressed print screen and open paint program

anonymous · Answer

whats next?

hartnn · Answer

paste it 
or ctrl+v

anonymous · Answer

this is really great tool! thank you

anonymous · Answer

attachment

anonymous · Answer

I posted it

hartnn · Answer

i think i am missing something here....
what we got id dy and not delta y

hartnn · Answer

*is

hartnn · Answer

for delta y , you use 
2(delta x)^2

anonymous · Answer

,mmmmmm...

hartnn · Answer

tried 0.18 for 1st and 4.8 for 2nd ??

anonymous · Answer

Woop! the second was correct! but not the first one

hartnn · Answer

i hope you already tried 4.8 for both ?

anonymous · Answer

i tried 4.8 for the first but no

hartnn · Answer

oh, that is linearization problem!

anonymous · Answer

yes, it is :)

hartnn · Answer

$y = f(\Delta x )+f'(\Delta x)(x-\Delta x)$

hartnn · Answer

$y = f(0.3 )+f'(0.3)(4-0.3)$

hartnn · Answer

$\Delta y= y-f(0.3)$

hartnn · Answer

f' = 4x 
f'(0.3) = 4*0.3= 1.2 
1.2 *(4-0.3) = 1.2 * 3.7=4.44

anonymous · Answer

is that special equation right? what is it called?
the answer is 4.444?

hartnn · Answer

that equation is used to make any non-linear equation as approximately linear.

hartnn · Answer

only 4.44

anonymous · Answer

the answer is still wrong

hartnn · Answer

1.2*0.3 = 3.6 
my last attempt...

hartnn · Answer

actually 0.36

anonymous · Answer

No it didnt work but thanks a lot!