**Geometric series :**

A series whose terms are in geometric progression is called geometric series.

To find the sum of n terms of the geometric series, we use one of the formulas given below.

s_{n} = a(r^{n} - 1)/(r - 1) if r > 1

s_{n} = a(1 - r^{n})/(1 - r) if r < 1

s_{n} = a/(1 - r) if r = 1

**Example 1 :**

Find the sum of the series

1 + 3 + 9 + ................. to 10 terms

**Solution :**

a = 1, r = 3 > 1 and n = 10

s_{n} = a(r^{n} - 1)/(r - 1) if r > 1

s_{10} = 1(3^{10} - 1)/(3 - 1)

s_{10} = (59049 - 1)/2

s_{10} = 59048/2

s_{10} = 29524

**Example 2 :**

A ball is dropped from a height of 6 m and on each bounce it bounces 2/3 of its previous height.

(i) What is the total length of the downward paths ?

(ii) What is the total length of the upward paths ?

(iii) How far does the ball travel till it stops bouncing?

**Solution :**

Distance covered in the downward path

= 6 + 4 + 8/3 + 16/9 + .............

a = 6 and r = 4/6 ==> 2/3

To find the sum of infinite series, we use the formula

s_{n} = a / (1 - r)

s_{n} = 6 / (1 - (2/3))

s_{n} = 6 / (1/3)

s_{n} = 18 m

(ii) Distance covered in the upward path

= 4 + 8/3 + 16/9 + ............

Here a = 4 and r = 2/3

s_{n} = a / (1 - r)

s_{n} = 4 / (1 - (2/3))

s_{n} = 4 / (1/3)

s_{n} = 12 m

(iii) Total distance covered = 18 + 12

= 30 m

After having gone through the stuff given above, we hope that the students would have understood how to find the sum of geometric series.

Apart from the stuff given in this section, if you need any other stuff in math, please use our google custom search here.

If you have any feedback about our math content, please mail us :

**v4formath@gmail.com**

We always appreciate your feedback.

You can also visit the following web pages on different stuff in math.

**WORD PROBLEMS**

**Word problems on simple equations **

**Word problems on linear equations **

**Word problems on quadratic equations**

**Area and perimeter word problems**

**Word problems on direct variation and inverse variation **

**Word problems on comparing rates**

**Converting customary units word problems **

**Converting metric units word problems**

**Word problems on simple interest**

**Word problems on compound interest**

**Word problems on types of angles **

**Complementary and supplementary angles word problems**

**Trigonometry word problems**

**Markup and markdown word problems **

**Word problems on mixed fractrions**

**One step equation word problems**

**Linear inequalities word problems**

**Ratio and proportion word problems**

**Word problems on sets and venn diagrams**

**Pythagorean theorem word problems**

**Percent of a number word problems**

**Word problems on constant speed**

**Word problems on average speed **

**Word problems on sum of the angles of a triangle is 180 degree**

**OTHER TOPICS **

**Time, speed and distance shortcuts**

**Ratio and proportion shortcuts**

**Domain and range of rational functions**

**Domain and range of rational functions with holes**

**Graphing rational functions with holes**

**Converting repeating decimals in to fractions**

**Decimal representation of rational numbers**

**Finding square root using long division**

**L.C.M method to solve time and work problems**

**Translating the word problems in to algebraic expressions**

**Remainder when 2 power 256 is divided by 17**

**Remainder when 17 power 23 is divided by 16**

**Sum of all three digit numbers divisible by 6**

**Sum of all three digit numbers divisible by 7**

**Sum of all three digit numbers divisible by 8**

**Sum of all three digit numbers formed using 1, 3, 4**

**Sum of all three four digit numbers formed with non zero digits**