This is the question-

part a) let g(x,y)= root (x^2-y^2)

find the differential dg of g

[ my answer is dg= x(dx)/root(x^2-y^2) - y(dy)/root(x^2-y^2)

where dx is the small change and dy is a small change too..

now part b) find an approx for root (13.4^2-11.7^2)

i took x= 13 and y = 11 and my dx=.4 and dy=.7

when i use my part a and sub them in i should get somewhere near 6.5 which i dont

HELP ME PLEASE