Question

1) find d^2f/dx^2
when f(x) = x e^-7y+5y

2) find d^2f/dx dy

when f(x) = x e^-8y+3y

Answer 1

two different questions here question (1) find d^2f/dx^2when f(x) = x e^-7y+5y


question (2) find d^2f/dx dy
when f(x) = x e^-8y+3y

Answer 2

deriveing twice I assume

Answer 3

do we do partials? or implicits?

Answer 4

well, since f(x) implies one variable id conjecture implicits

Answer 5

hmm since its wrt x and both are linear wrt x then the 2nd derivatives are 0

Answer 6

\[ x e^{-7y} + 5y\]
by chance?

Answer 7

oh i was assuming partial

Answer 8

those groupings are a pain if you dont get them right

Answer 9

x e^(-7y) + 5y

x' e^(-7y)+ x e^(-7y)' + 5 y'

e^(-7y) -7x e^(-7y) y' + 5 y'

then again

Answer 10

i have loads of these, need to be handed in ten minutes haha

Answer 11

the second one there suggests partials but its only a single variable

Answer 12

amistre, you are finding dy/dx not df/dx though

Answer 13

f(x) assumes that all variables are functions of x, so y = y(x)

Answer 14

the 2nd on tho says f(x) and wants f_xy

Answer 15

i think it should be written f(x,y) otherwise it would have asked for dy^2/dx

right?

Answer 16

i think there might be some confusion as to whether f(x) IS y rather than written out is a rule with x(x) and y(x)

Answer 17

hard for me to parse the intricate details tho :)

Answer 18

agreed...salman little help?

Answer 19

its d^2f/dx dy

the f(x)=xe^-8y+3y

sorry chaps, this is the only info i have

Answer 20

ok, then assuming f(x) is not y, y is just another variable

df/dx = e^-8y

d/dy e^-8y = -8*e^-8y

Answer 21

for part a)
df/dx = e^-7y
d/dx e^-7y = 0