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Mathematics 8 Online
zarkam21:

Help with what I did wrong here

zarkam21:

1 attachment
zarkam21:

1 attachment
zarkam21:

I started doing the corrections but I don't know whats next

jhonyy9:

sorry but i dont understand your work on the first one

jhonyy9:

but this is very easy

zarkam21:

The first one is wrong. I just put a picture so you could see the problem. the second picture is the beginning of my corrections but I do not know where to go from there

jhonyy9:

ok. now you talk about what question ? i ve said question 3 /a

zarkam21:

no question 4

zarkam21:

?

jhonyy9:

in the 4th line where you elimined the exponent of e ?

zarkam21:

@SmokeyBrown

SmokeyBrown:

Ok, so you want to find the half-life, right? So, we'd need to find the value of t when W(t) = (W0)/2, right? In other words, the amount of time it takes for the amount of isotope to be cut in half from the starting point

zarkam21:

Okay and the starting point would be 0.002?

SmokeyBrown:

To start out, we can write our equation as follows: \[W _{0}/2 = W _{0} \times e ^{-0.002t}\] We could divide by W0 on both sides, leaving us with \[1/2 = e ^{0.002t}\] Then, you'd just have to solve for t. I think you use logs for this?

zarkam21:

=-346.57

zarkam21:

would the units be meter

SmokeyBrown:

Nah, my dude, half-life is a time, so the units would be years

zarkam21:

oh okay but am I right with the positive and btw Imma girl lol

zarkam21:

with the negative I meant?

zarkam21:

because it is a time frame

SmokeyBrown:

Oh, true

zarkam21:

like would it still be -346.57 yrs

SmokeyBrown:

Haha, no that wouldn't really make sense. Uh, let me check that calculation

zarkam21:

okay

SmokeyBrown:

So we'd start out by taking the natural log of both sides. That gives us -0.693 = - 0.002t If we divide both sides by -0.002, we get 346.5 = t I see that I forgot a negative sign in my second equation. It should be -0.002t, not 0.002t. That's my bad

zarkam21:

okay so it would be 345.5 = t which is also years?

zarkam21:

I mean this would be the half life?

zarkam21:

You there

SmokeyBrown:

Yup, that's right

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