My little sister's math problem - how to solve with only what she knows already (algebra I)?

[stultus]

(1/3)^x = 27^(x+8), solve for x.

This is for algebra one - my little sister has to do this for homework (she IM'd it to me).

I would take the log, go:

x log 1/3 = x+8 log 27

x/(x+8) = log 27 / log (1/3)

(use calc for log)

x/(x+8) = -3

x = -6

Their class apparently has never heard of logs yet. How in the world do you do this without logs?

 

[GeneValgene]

here's what they want you to see:

27 is the same thing as (1/3)^-3

therefore by setting the exponents equal to each other

you get -3(x+8) = x

solve for that and get teh same thing you did

 

[sniperbob]

if all else fails, you can always do "graph both function and see where they intercept" method.

 

[Savij]

(1/3)^x = 27^(x+8), solve for x.

1/3 = 3^ -1

27 = 3^ 3

so

3^(-x) = 3^(3*(x+8))

-x = 3x + 24

-24 = 4x

x = -6

enjoy

 

[Savij]

doh!

too late

 

[nicowju]

I'd say restate each base in terms of powers of 3, so the first would be 1/3=3^-1, and 27=3^3

Then, you get something like this: 3^(whatever1)=3^(whatever2), and you just set the exponents equal and solve for x

 

[stultus]

Ah, good. It's been too long since I had to do any math 😉 Thanks!

 

[illusion88]

Originally posted by: sniperbob
if all else fails, you can always do "graph both function and see where they intercept" method.

my favorite method!
Fvck working, I got an expensive graphing calculator that will do it for me!

 

[Lithium381]

if your sis is in algebrea.......hmmmmm pics?!!?

 

[jagr10]

Yup people have already said what i was gonna suggest. Use a common base and go from there.

 

[m2kewl]

Originally posted by: Lithium381
if your sis is in algebrea.......hmmmmm pics?!!?

yer going to hell! 😉😛

 

[NutBucket]

Originally posted by: Lithium381
if your sis is in algebrea.......hmmmmm pics?!!?

LOL😛

 

[ElFenix]

man i don't remember that crap

 

[stultus]

Originally posted by: Lithium381
if your sis is in algebrea.......hmmmmm pics?!!?

I would just like to say that my brother and I had a bet going on to see which forum, ATOT or Genmay would be more helpful. I told him that on Genmay I'd expect the first 5 replies to be "pics?" and nobody would say anything useful. So within 5 min on here, we have an answer and NOT ONE dumb comment. I proudly showed him the thread that within 5 min I had an answer. Then, he posts the exact same thread on genmay, and we get only one stupid reply and an answer in 6 min.

I was so proud of AT.

And then Lithium came along. 😛

 

[stultus]

Thread on genmay: here

 

[m2kewl]

Originally posted by: stultus

Originally posted by: Lithium381 if your sis is in algebrea.......hmmmmm pics?!!?

I would just like to say that my brother and I had a bet going on to see which forum, ATOT or Genmay would be more helpful. I told him that on Genmay I'd expect the first 5 replies to be "pics?" and nobody would say anything useful. So within 5 min on here, we have an answer and NOT ONE dumb comment. I proudly showed him the thread that within 5 min I had an answer. Then, he posts the exact same thread on genmay, and we get only one stupid reply and an answer in 6 min. I was so proud of AT. And then Lithium came along. 😛

LMAO! Genmay is bbbbbaad!

<married with children voice> THANKS Lithium!!! </married with children voice>