Chapter 9 - Quadratic Functions and Equations - 9-5 Completing the Square - Practice and Problem-Solving Exercises - Page 579: 19

vertex: $( -2,- 20)$

$y=x^2+4x-16$ ...(1) compare it with standard equation: $y=a(x-h)^2+k$ with vertex$(h,k)$ Consider right side $x^2+4x=16$ To complete the square add $(\frac{b}{2})^2=(\frac{4}{2})^2=4$. $x^2+4x+6=16+4=20$ $(x+2)^2=20$ Thus, equation becomes: $y=(x+2)^2-20$ Compare it with the standard form, we get vertex: $( -2,- 20)$