{"id":4762,"date":"2021-08-25T15:09:23","date_gmt":"2021-08-25T15:09:23","guid":{"rendered":"https:\/\/mathemerize.com\/?p=4762"},"modified":"2021-11-17T17:47:44","modified_gmt":"2021-11-17T12:17:44","slug":"formula-for-geometric-progression-gp","status":"publish","type":"post","link":"https:\/\/mathemerize.com\/formula-for-geometric-progression-gp\/","title":{"rendered":"Formula for Geometric Progression (GP)"},"content":{"rendered":"
Here you will learn what is geometric progression and formula for geometric progression with examples.<\/p>\n
Let’s begin –<\/p>\n
A sequence of non-zero numbers is called a geometric progression (GP) if the ratio of a term and the term preceding to its always a constant quantity.<\/p>\n
The constant ratio is called the common ration of the GP.<\/p>\n
\nIn other words, a sequence \\(a_1\\), \\(a_2\\), \\(a_3\\) …….. \\(a_n\\) , …….. is called a geometric progression if<\/p>\n
\\(a_{n+1}\\over a_n\\) = constant for all n \\(\\in\\) N<\/p>\n<\/blockquote>\n
Example : The sequence 4, 12, 36, 108, is a GP , because<\/p>\n
\\(12\\over 4\\) = \\(36\\over 12\\) = \\(108\\over 36\\) = ….. = 3, which is a constant.<\/p>\n
Clearly, this sequence is a GP with first term 4 and common ratio 3.<\/p>\n
Also Read<\/strong> : Formula for Arithmetic Progression (AP)<\/a><\/p>\n
Formula for Geometric Progression<\/h2>\n
(a) General Term of a GP<\/h3>\n
Let a be the first term and r be the common ratio of a GP. Then its nth term or general term is \\(ar^{n-1}\\)<\/p>\n
\ni.e\u00a0 \u00a0\\(a_n\\) = \\(ar^{n-1}\\)<\/p>\n<\/blockquote>\n
Note :\u00a0<\/strong>The whole GP can be written as a, ar, \\(ar^2\\), …… , \\(ar^{n-1}\\)\u00a0 or\u00a0 a, ar, \\(ar^2\\), …… , \\(ar^{n-1}\\), …… according as it is finite or infinite.<\/p>\n
(b) nth term from the end of a finite GP<\/h3>\n
(i) The nth term from the end of a finite GP consisting of m terms is \\(ar^{m-n}\\), where a is the first term and r is the common ratio of the GP.<\/p>\n
\n\\(\\because\\)\u00a0 \u00a0nth term from the end = (m – n + 1)th term from the beginning\u00a0<\/p>\n
\u00a0= \\(ar^{m-n}\\)<\/p>\n<\/blockquote>\n
(ii) and the nth term from the end of a GP with last term l and common ratio r is given by\u00a0<\/p>\n
\n\\(a_n\\) = l\\(({1\\over r})^{n-1}\\)<\/p>\n<\/blockquote>\n
Clearly when we look at the terms terms of a GP from the last term and move towards the beginning we find that the progression is a GP with the common ration 1\/r.<\/p>\n
\nSo, nth term from the end = l\\(({1\\over r})^{n-1}\\)<\/p>\n<\/blockquote>\n
Also Read<\/strong> : Sum of GP Series Formula | Properties of GP<\/a><\/p>\n\n\n
Example : <\/span>Find the 9th term and the general term of the progression \\(1\\over 4\\), \\(-1\\over 2\\), 1, -2, ……<\/p>\n
Solution : <\/span>The given progresion is clearly a gp with the first term a = \\(1\\over 4\\) and common ratio r = -2.
\n\\(\\therefore\\) 9th term = \\(a_9\\) = \\(ar^{(9-1)}\\) = \\(1\\over 4\\)\\((-2)^{8}\\) = 64
\nand, General term = \\(a_n\\) = \\(ar^{(n-1)}\\) = \\(1\\over 4\\) \\((-2)^{n-1}\\) = \\((-1)^{n-1}\\) \\(2{n-3}\\)
<\/p>\n\n\n
\nRelated Questions<\/h3>\n
If the 4th and 9th terms of a G.P. be 54 and 13122 respectively, find the G.P.<\/a><\/p>\n