# Math Help - Finding a Quadratic Equation from Mulitple Points

1. ## Finding a Quadratic Equation from Mulitple Points

I know their are quite a few of these questions on the net and I have looked at them, but I havent really been able to properly understand how they actually work.

I have to find what x when y=.11, so im guessing that I need to find the quadratic equation, right???
NOTE: Im not 100% sure this is a quadratic equation. If it isn't, any suggestions on how to solve it.

x y

0 16
1 8
2 4
3 2
4 1
5 0.5
6 0.25
7 0.125
8 0.0625

2. Hi,
It's not a quadratic function, it is rather $y=2^{4-x}$.

3. Can I use this to solve my problem???

4. yes, take logarithm of both sides to express x:
$\ln y=\ln (2^{4-x}) = (4-x)\ln2$, so $x=4-\frac{\ln y}{\ln 2}$.

I don't know what ".11" is, never seen it. Can you explain pls?

5. Sorry. Its part of a word problem where I have to find the age (in carbon-14 half lives) of a sample with a rate of disintergration of C-14 of .11 disintergrations/min/gram. I ve been given the first the first 3 numbers of each variable and I used Excel to copy the formula.

Half Life Disintergration rate
0 16
1 8
2 4
(Note 1 C-14 Half-Life = 5730 Years before present)