[填空题]
When a ball is thrown dqloymqt +2a /av2 zr8xv66z58aaw8 i from th-nc nw4 hq/qsj,6r9/sv w/rlhe top of a tall building, its height above the ground afte/wj4qwlsv9 -rsc/hrn6, nh /qr 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
