Thomas' Calculus 13th Edition

Equate $f(x,y)=c$ for each value of c $\left[\begin{array}{llll} c=-3 & x+y-1=-3 & \Rightarrow & y=-x-2 \\ c=-2 & x+y-1=-2 & \Rightarrow & y=-x-1\\ c=-1 & x+y-1=-1 & \Rightarrow & y=-x\\ c=0 & x+y-1=0 & \Rightarrow & y=-x+1\\ c=1 & x+y-1=1 & \Rightarrow & y=-x+2\\ c=2 & x+y-1=2 & \Rightarrow & y=-x+3\\ c=3 & x+y-1=3 & \Rightarrow & y=-x+4 \end{array}\right]$ Lines with slope $-1$, with y-intercepts $-2,-1,...,4$