Arithmetic sequence question?

[reyrmart]

I have been able to find the nth term for a specific sequence: for example 3, 7/3, 5/3.... where a1=3 and d=-2/3. My question is : What term is -27? Please help !

 

[stapel]

I have been able to find the nth term for a specific sequence: for example 3, 7/3, 5/3.... where a1=3 and d=-2/3. My question is : What term is -27?

What formula(s) have they given you? When you found the n-th term, what did you use? Can you try plugging the given values in, and trying to solve for the value of n, given the value of a_n (rather than solving for the value of a_n, given n)?

 

[pka]

I have been able to find the nth term for a specific sequence: for example 3, 7/3, 5/3.... where a1=3 and d=-2/3. My question is : What term is -27? Please help !

\(\displaystyle \dfrac{9}{3}-\dfrac{2(n-1)}{3}=-27\) solve for \(\displaystyle n\).

 

[Quaid]

Hi Rey:

I see that pka answered stapel's question, by posting the formula that he used, including his substitutions.

I'm still interested to see your answer.

How did you find the nth term? Please show us your formula.

Cheers

 

[Dale10101]

Dollars and sense perspective

27 checks on a bank account that has an initial balance of zero ... The first check adds three dollars, the remaining 26 checks draw out 2/3 dollars each. What is your negative balance? What is the shortcut formula you used to intuitively compute that result? How does your formula compare to the of the one given by Pka? How about the one in your book that starts a_n = ....? Examples like this give meaning to the formulas and make them easier to remember. Good luck