Thomas' Calculus 13th Edition

$y=-x$
The point-slope equation of a line containing the point $(x_{1},y_{1})$, with slope $m$ is $y=y_{1}+m(x-x_{1})$ Given $(x_{1},y_{1})=(-1,1)$ and $m=-1$ $y=1+(-1)(x-(-1)$ $y=1-(x+1)$ $y=1-x-1$ $y=-x$