## anonymous 5 years ago Someone help?...:The vertex of y = 9 - 8x - x2 is (-4, 25) True or False?

1. anonymous

true...

2. anonymous

$y=9-8x-x^2=25-16-8x-x^2=25-(4+x)^2$ $\Rightarrow\quad (-4,25)\,\,is\,vertex$

3. anonymous

he added 16 for (4+x)^2, that's why he has to subtract 16 again: 25 = 9 - (-16)