## Calculus: Early Transcendentals 8th Edition

All the points on the line $y=x+1$
Formula to calculate the maximum rate of change of $f$: $D_uf=|\nabla f(x,y)|$ $\nabla f(x,y)=\lt 2x-2,2y-4 \gt$ Direction vector: $\lt 1,1 \gt$ Thus, $\lt 2x-2,2y-4 \gt=n\lt 1,1 \gt$ This implies $n=2x-2, n=2y-4$ and $2x-2=2y-4$ Hence, the required answer is: All the points on the line $y=x+1$