Question

How do you know if y=16−4x2 opens up or down?

Answer 1

y= 16- 4x2

y= 16-8x

16=8x

x=16/8
x =2

Answer 2

let the equation of parabola be

$a {x}^{2} + bx + c = 0$

to know whether the parabola looks up or down, then go for the sign of "a"

if, a>0 (parabola faces upward)

if, a<0 (parabola faces downward)

hope it helps（＾＿－）≡★