# math+ confused!

posted by
**eva!** on
.

okay the question is as follows:

write the first three teerms of tn= 5(2)^ n-1. what is the value of

tn/tn-3?

I did not get I asked my teacher and he said:

plug in n=1, n=2, n=3, to find t_1, t_2, t_3.

plug in n-3 and n separately. then take the ratio of the terms.

I am totally confused now could you probably explain to me waht my teacher is telling me? thanks!

Are you confused with both parts, or just the second part?

For the first part, substitute variable n with the number 1. Then with 2, and last with 3.

t(n) = 5(2)^(n-1)

t(1) = 5(2)^(1-1)

t(2) = 5(2)^(2-1)

t(3) = 5(2)^(3-1)

Of course, each of those answers can be simplified to a number.

Similarly with n and (n-3):

t(n) = 5(2)^(n-1)

t(n-3) = 5(2)^((n-3)-1)

Setup a fraction and simplify to find the ratio.

Your teacher gave you the correct instructions. Basically this is what you're expected to do.

You have t_{n} = 5*2^{n-1}

So the substitution part is

t_{1} = 5*2^{1-1} = 5*1

t_{2} = 5*2^{2-1} = 5*2

t_{3} = 5*2^{3-1} = 5*4

The second part is

t_{n}/t_{n-3} = 5*2^{n-1}/5*2^{n-4}

The 5's cancel so you have

t_{n-1}/t_{n-3} = 2^{n-1}/2^{n-4} =

2^{(n-1)-(n-4)} = 2^{4-1} = 2^{3}

What this is telling you is that the n^{th} term is eight times the one three places prior to it.

Wow, great use of subscript and superscript.

Thnx, and thank you of enabling them.

Be sure to let us know if/when other tags are enabled.

Subscripts and superscripts are great for complex problem like this but they are a pain to use except when clarity overrides the inconvenience.

i just want to know what this means in math-< >?

love,

jessica

What other tags do you need?

I'm always looking for ways to improve the site.

I don't know if these are available, but having the Greek alphabet would help a lot. In pob/stats we use beta, chi, mu and sigm a lot. In geometry we especially use pi and theta. In calculus upper and lower case delta. Anyway it would be nice to use those letters instead of writing them out.

Also having a tag for fractions would make rational expressions look a lot nicer. In LaTeX we use [] for the tags and the tag for fractions looks like [frac]{numerator}{denominator}[/frac], where the expressions are enclosed with braces. There are a lot of special symbols that are nice to have too, like intersection and union in set theory and the little symbol for an angle. I don't know if it's asking too much to include the integral symbol.

I do know that a number of sites that answer math questions have enabled an abbreviated version of LaTeX, some use a fairly complete one.

Another thing that would be nice to have is a preview screen. If there was a button that allowed us to preview before posting we'd probably catch a lot more typos that way...just a thought.

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