Chapter 9 - Quadratic Functions and Equations - 9-8 Systems of Linear and Quadratic Equations - Practice and Problem-Solving Exercises - Page 585: 21

$(-11,-91)$, $(9,-71)$

$-x^2-x+19=y$ $x=y+80$ $x=y+80$ $x-80=y+80-80$ $x-80=y$ $-x^2-x+19=y$ $-x^2-x+19=x-80$ $-x^2-x+19-x+80=x-80-x+80$ $-x^2-2x+99=0$ $-(x^2+2x-99)=0$ $-(x+11)(x-9)=0$ $x+11=0$ $x=-11$ $x-9=0$ $x=9$ $x=y+80$ $-11=y+80$ $-11-80=y+80-80$ $-91=y$ $x=y+80$ $9=y+80$ $9-80=y+80-80$ $-71=y$