forming the equation

G

Guest

Guest
I don't get how you form this equation.

The time is takes for half of a sample of a radioactive isotope to decay is called the half life. Iodine-131 has a half-life of 8 days.

a) Write an equation to determine the amount of iodine-131 remaining in a sample after n half lives.

I get it's a geometric sequence, and that the ratio is .5 that's all.

Annaaaaaaaaaaaa
 
That's pretty much all there is to get. What keeps you from writing down the answer?

I = Initial Amount
n = Half-lives elapsed

Start - Day 0: I*½<sup>0</sup> = I*1 = I -- Good, that's where we started.
Day 1: I*½<sup>1</sup> = I*½ = I/2
Day 2: I*½<sup>2</sup> = I*¼ = I/4
...
Day t - just some number of days into the future: I*½<sup>t</sup>

OK, where does that leave us?
 
well I jsut don't get how the answer is only to the power of n and not how the equation is usually, which is to the power of n-1
 
It's tough to overcome preconceived ideas. What's an example of a "usual" outcome?

The index doesn't much matter. Just pick something that works unless there is some compelling reason to do otherwise.
 
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