#Partial Derv, Part C?

33 messages · Page 1 of 1 (latest)

lost oyster
#

I'm able to do part A and B, but part C is tripping me up

#

The last part of part C

surreal spade
#

you would take the derivative relative to x, and then the derivative relative to y of that:
∂/∂y(∂f/∂x)

#

and if the function is continuous, as well as the partial derivative relative to x, and the partial derivative relative to y, then that should be the same as ∂/∂x(∂f/∂y)

#

@lost oyster

lost oyster
#

ohh

#

I see

#

Thank you

surreal spade
#

the detail I added about continuity links into mean value theorem, when you get to real analysis then you'll learn about how it works and why it's related with calc

lost oyster
#

ohhh

surreal spade
lost oyster
# surreal spade np

I put it into a calc and it gave me -6x? But when I did it on paper I got 8x^3 -6x

#

It's the 3rd line

#

From the top

surreal spade
#

one sec:
first derivative relative to x:
(-2x)(y-2x²)-(4x)(y-x²)
derivative relative to y:
-2x-4x

#

I used product rule first

lost oyster
surreal spade
#

-2xy+4x³-4xy+4x²
8x³-6xy
and then relative to y
8x³ is constant, so is 0
-6xy→-6x

lost oyster
#

wait

surreal spade
#

what

lost oyster
#

I did it again and got 1

surreal spade
#

now you have ∂³f/∂x∂y²

lost oyster
#

OHHH

surreal spade
#

how did you get 1

#

it should be 0

#

what

lost oyster
#

you're right

#

the derv of a constant is 0

#

but I see what I was doing wrong

surreal spade
#

yes lmao

lost oyster
#

I wasn't using the given f(x,y) lmao