Answer:
± 1/4 sqrt((400-y)) =t
Explanation:
Y=-16t^2 + 400
Subtract 400 from each side
y - 400 = -16t^2 +400-400
y-400 = -16t^2
Divide by -16t^2
(y-400)/-16 = t^2
(400-y)/16 = t^2
Take the square root of each side
±sqrt((400-y)/16) =sqrt(t^2)
±sqrt((400-y)) / sqrt(16) =t
± 1/4 sqrt((400-y)) =t