Given the following points find the best-fit quadratic model:

(1,211),(2,215),(4,127), and (5,35).

We can use technology or solve the following system of equations:

a + b + c = 211

4a + 2b +c = 215

16a +4b +c = 127

Solving the system yields a=-16,b=52 and c=175.

**So a model that fits the points is `h=-16t^2+52t+175` **

**Check: if t=5 `h=-16(5)^2+52(5)+175=35` **

Then we need to find the time(s) when the rocket is at 100ft.

`-16t^2+52t+175=100 ==> -16t^2+52t+75=0`

We can use the quadratic formula to solve:

`t=(-52+-sqrt(52^2-(4)(-16)(75)))/(2(-16))`

`t=(-52+-sqrt(7504))/(-32)`

`t~~(-52+86.63)/(-32)` or `t~~(-52-86.63)/(-32)` so

**`t~~-1.08` or `t~~4.33` The first answer implies a time before launch, so the time that the rocket hits 100 ft is approximately 4.33 seconds after launch.**