Question

giving fan and medal!!!!
how to find the number of term in a sequence?

Answer 1

@ganeshie8 can u plz help me?

Answer 2

@mathmale

Answer 3

@zaibali.qasmi ?

Answer 4

What's the sequence?

Answer 5

-9 - 3 + 3 + 9 + ... + 81

Answer 6

That's not a sequence... do you mean series?

Answer 7

oh,yes:)

Answer 8

Okay, so you have to find the sum of the series, is that it?

Answer 9

yes,but do u know how to find the number of terms in this series?is there a formula for it?

Answer 10

There is (look up arithmetic sequences/progressions/series), but I usually approach this sort of problem by deriving the formula and figuring out a pattern between the terms in the sum.

Let \(a_n\) denote the \(n\)th term in the series, so \(a_1=-9\), \(a_2=-3\), and so on.
\[a_1=-9\\
a_2=-9+6=-3\\
a_3=-9+6+6=-3+6=3\\
a_4=-9+6+6+6=3+6=9\\
~~~~~\vdots\\
a_n=-9+(n-1)6\]

Answer 11

ok.i am with u;)

Answer 12

You want to find the highest value of \(n\). You know that the last term is \(\color{blue}{a_n=81}\), and \(\color{red}{a_1=-9}\).

So,
\[\color{blue}{81}=\color{red}{-9}+(n-1)6\]
Solve for \(n\), and you'll have the number of terms in the series.

Answer 13

Got it?

Answer 14

yes, i totally understand it!thnku dooooooo much:)btw,what math level r u?

Answer 15

so much

Answer 16

I'm a student, and I'll always be a student :P

Answer 17

haha!!

Answer 18

@SithsAndGiggles I'm a student, and I'll always be a student :P
very nice statement here^_^