1. The problem statement, all variables and given/known data
rate of change of f(x,y) = x/(1+y) in the direction (i-j) at the point (0,0)
2. Relevant equations
3. The attempt at a solution
grad(f(x,y)) = 1/(y+1)i - x/(y+1)^2j
Du = ( f_x, f_y ) dot ( 1, -1 )
Du = (y+x+1)/(y+1)^2
Wolfram and the answer sheet is telling me that there should be a sqrt(2) in the denominator, but I can't figure out where it comes from, thanks.
rate of change of f(x,y) = x/(1+y) in the direction (i-j) at the point (0,0)
2. Relevant equations
3. The attempt at a solution
grad(f(x,y)) = 1/(y+1)i - x/(y+1)^2j
Du = ( f_x, f_y ) dot ( 1, -1 )
Du = (y+x+1)/(y+1)^2
Wolfram and the answer sheet is telling me that there should be a sqrt(2) in the denominator, but I can't figure out where it comes from, thanks.
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