[填空题]
When a ball is throwrru,aag8bi0l ;o - r)u 7l*k hdjkf6gs9u)hy,n from the top of a tall building, its height above the groundk9,6hkf*j) ydl hug 7s after t seconds is given by
s(t)=$at^2$+bt+c, where a,b,c∈R and s(t) is measured in metres. After 1 second, the ball is 84.3 m above the ground; after 2 seconds, 93.9 m; after 8 seconds, 42.3 m.
1.(1)Write down a system of three linear equations in terms of a, b and c.
(2)Hence find the values of a, b and c. a = b = c =
2.Find the height of the building. s = m
3.Find the time it takes for the ball to hit the ground. t ≈ seconds
