3) Given f(x, y) = x4y2 – 5x - 7y + 8, find:
a) fx b) fxx c) fxy d) fy e) fyy f) fyx

Question

3)	Given f(x, y) = x4y2 – 5x - 7y + 8, find:  
a)	fx     b) fxx      c) fxy     d) fy    e) fyy    f) fyx

amistre64 · Answer

practice for getting you into the hang of partial derivatives eh

anonymous · Answer

$$Given f(x, y) = x^4y^2 – 5x - 7y + 8$$

amistre64 · Answer

consider the non variable to be a constant

anonymous · Answer

yea pretty much

amistre64 · Answer

$$fx = 3x^3 y^2-5+0+0$$

amistre64 · Answer

do you see why?

amistre64 · Answer

fxx just means to do that again; (fx)x

amistre64 · Answer

then just play back and forth as the conditions require to get the hang of it :)

amistre64 · Answer

4x^3 .. my typo

anonymous · Answer

i thought that was fx and i didnt get wyou wrote 0,0

amistre64 · Answer

to organize this; do an fx and a fy

amistre64 · Answer

ok ... what do you know about partial derivatives?

anonymous · Answer

nothing ....

amistre64 · Answer

$$x^4y^2 – 5x - 7y + 8$$
to do this with respect to x; consider everything that is not an "x" as a constant value ...
$$x^4B – 5x - B + B$$
now derive
$$fx=4x^3B – 5 - 0 + 0$$
and change back to the y value for a finish
$$fx=4x^3y^2 – 5 - 0 + 0$$

amistre64 · Answer

what do you know of just normal derivatives?

amistre64 · Answer

to do fy just consider all x parts to be constant

$$f=By^2 – B - 7y + B$$
derive with respect to y
$$f=2By – 0 - 7 + 0$$
change back to your xs and get rid of the zeros
$$f=2x^4y - 7$$

amistre64 · Answer

i fyou know how to do "normal" derivatives; this is the same process; only we consider the stuff that isnt under the gun as a constant; as if it was just another number and not a variable