# What is the vertex of y= -x^2+16x + 21?

Jun 30, 2018

(8,85)

#### Explanation:

$\frac{- b}{2 a}$ gives the x coordinate for the vertex

$\frac{- 16}{2 \times - 1} = \frac{- 16}{- 2} = 8$

Put x=8 into the equation

$y = - {8}^{2} + 16 \times 8 + 21$

$y = - 64 + 128 + 21$

$y = 85$