Monday

November 24, 2014

November 24, 2014

Posted by **Anonymous** on Thursday, April 17, 2008 at 2:32pm.

(a)prove that the series is an AP, stating the first term and the common difference;

(b)find the sum of the terms from the 3rd to the 12th inclusive

2) In an AP the 6th term is half the 4th term and the 3rd term is 15.

(a)Find the first term and the common difference;

(b)How many terms are needed to give a sum that is less than 65?

Please help

- Math -
**Reiny**, Thursday, April 17, 2008 at 3:01pmIsn't t(n) = S(n) - S(n-1)

(e.g. the sixth term is sum of 6 terms minus the sum of 5 terms)

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

= 4n - 3

so from that you can now find any of the terms

notice t(1) = a = 1

d = 4

2) "the 6th term is half the 4th term"

----> a+5d = 1/2(a+3d)

"the 3rd term is 15" -----> a+2d = 15

solve these two equations.

**Answer this Question**

**Related Questions**

math - 1) If the sum of the first n terms of a series is Sn where Sn=2nē-n, (a)...

Math - the sum of the first n terms of an arithmetic series is -51. the series ...

Math. - The first term of a geometric series is 4 and the sum of the first three...

Algebra - In an arithmetic series, the terms of the series are equally spread ...

math - the "k"th term of a series, Sk=a 1-r^k/1-r, is the sum of the first "k" ...

math studies - An arithmetic series has a first term of -4 and a common ...

Geometric series - The sum of the first five terms of a geometric series is 186 ...

arithmetic - In an arithmetic series, the terms of the series are equally spread...

math B30 - If the seventh term of a geometric series is 192, and the first term ...

Math question - In an arithmetic series, the 15th term is 43 and the sum of the ...