Originally Posted by

**DoesNotCompute** Hi Guys,

this may seem like a very simple question to some of you.. but im struggling.. could someone please help me derive this:

f(x,y) = ln(x-3y)

Chain rule?.. if so ive confused myself with the x's and the y's

basicly ive been asked to find the linear approximation of that function at (7,2) and then use it to approximate f(6.9, 2.06).. could someone please confim the below process?

Find f(7,2)

Find f ′(x,y)

Find f ′(7,2)

Use formula for linear approximation near the point a .... f(x) ≈ f(a) + f ′(a) (x - a) not sure about this part.. what happened to the y's?

Substitute a = 7

then im unsure...

any help would be much appricated :-)