{"id":4015,"date":"2021-08-13T20:51:48","date_gmt":"2021-08-13T20:51:48","guid":{"rendered":"https:\/\/mathemerize.com\/?p=4015"},"modified":"2021-11-17T17:55:03","modified_gmt":"2021-11-17T12:25:03","slug":"formula-for-sum-of-ap-series","status":"publish","type":"post","link":"https:\/\/mathemerize.com\/formula-for-sum-of-ap-series\/","title":{"rendered":"Formula for Sum of AP Series | Properties of AP"},"content":{"rendered":"
Here, you will learn what is arithmetic progression (ap) and formula for sum of ap series and properties of ap.<\/p>\n
Let’s begin –<\/p>\n
The indicated sum of the terms of a sequence. In the case of a finite sequence \\(a_1\\), \\(a_2\\), \\(a_3\\),………,\\(a_n\\) the corresponding series is \\(a_1\\) + \\(a_2\\) + \\(a_3\\) + ……… + \\(a_n\\) = \\({\\sum_{k=1}^{n}a_k}\\). This series has a finite or limited numbers of terms and is called a finite series.<\/p>\n
A.P. is a sequence whose terms differ by a fixed number. This fixed number is called the common difference. If a is the first term & d the common difference, then A.P. can be written as<\/p>\n
a, a + d, a + 2d, ………, a + (n – 1)d, ……..<\/p>\n
\n\\(T_n\\) = a+(n-1)d,<\/p>\n
where d = \\(t_n\\) – \\(t_{n-1}\\)<\/p>\n<\/blockquote>\n
(b)\u00a0 The sum of the first n terms<\/h3>\n
\n\\(S_n\\) = \\(n \\over 2\\)[2a + (n-1)d]<\/p>\n
\\(S_n\\) = \\(n \\over 2\\)[a + l]\u00a0<\/p>\n
where l is \\(n^{th}\\) term.<\/p>\n<\/blockquote>\n
Also Read<\/strong> : Sum of GP Series Formula | Properties of GP<\/a><\/p>\n
Note :<\/strong><\/p>\n
(i)\u00a0 \\(n^{th}\\) term of an A.P. is of the form An + B i.e. a linear expression in ‘n’, in such a case the coefficient of n is the common difference of the A.P. i.e. A.<\/p>\n
(ii)\u00a0 Sum of first ‘n’ terms of an A.P. is of the form \\(An^2\\) + Bn i.e. a quadratic expression in ‘n’, in such case the common difference is twice the cofficient of \\(n^2\\). i.e. 2A<\/p>\n
(iii)\u00a0 Also \\(n^{th}\\) term \\(T_n\\) = \\(S_n\\) – \\(S_{n-1}\\)<\/p>\n\n\n
Example : <\/span>If (x + 1), 3x and (4x + 2) are first three terms of an A.P. then its \\(5^{th}\\) term is-<\/p>\n
Solution : <\/span>(x + 1), 3x, (4x + 2) are in AP
\n\t\t => 3x – (x + 1) = (4x + 2) – 3x => x = 3
\n\t\t => a = 4, d = 9 – 4 = 5
\n\t\t => \\(T_5\\) = 4 + (4)5 = 24
\nHence, its \\(5^{th}\\) term is 24
<\/p>\n\n\nProperties of AP<\/h2>\n
(a) If each term of an A.P. is increased, decreased, multiplied or divided by the some nonzero number, then the resulting sequence is also an A.P.<\/p>\n
(b) <\/p>\n
Three numbers in A.P. : a-d, a, a+d<\/strong><\/p>\n
Four numbers in A.P. : a-3d, a-d, a+d, a+3d<\/strong><\/p>\n
Five numbers in A.P. : a-2d, a-d, a, a+d, a+2d<\/strong><\/p>\n
Six numbers in A.P. : a-5d, a-3d, a-d, a+d, a+3d, a+5d<\/strong> etc.<\/p>\n
(c) The common difference can be zero, positive or negative.<\/p>\n
(d) \\(k^{th}\\) term from the last = (n – k+1)th term from the beginning (If total number of terms = n).<\/p>\n
(e) The sum of the two terms of an AP equidistant from the beginning & end is constant and equal to the sum of first & last terms. => \\(T_k\\) + \\(T_{n-k+1}\\) = constant = a + l.<\/p>\n
(f) Any term of an AP (except the first) is equal to half the sum of terms which are equidistant from it. \\(a_n\\) = (1\/2)(\\(a_{n-k}\\) + \\(a_{n+k}\\)), k < n <\/p>\n
(g) If a, b, c are in AP, then 2b = a + c. <\/p>\n\n\n
Example : <\/span> Four numbers are in A.P. If their sum is 20 and the sum of their squares is 120, then the middle terms are-<\/p>\n
Solution : <\/span>Let the numbers are a-3d, a-d, a+d, a+3d
given, a-3d + a-d + a+d + a+3d = 20\n\t\t => 4a = 20 => a=5
and \\((a-3d)^2\\) + \\((a-d)^2\\) + \\((a+d)^2\\) + \\((a+3d)^2\\) = 120
\n\t\t => 4\\(a^2\\) + 20\\(d^2\\) = 120
\n\t\t => 4 x \\(5^2\\) + 20\\(d^2\\) = 20 => \\(d^2\\) = 1 => d = \\(\\pm\\)1
\n\t\t Hence numbers are 2,4,6,8 or 8,4,6,2
<\/p>\n\n\n
\nRelated Questions<\/h3>\n
If 100 times the 100th term of an AP with non-zero common difference equal to the 50 times its 50th term, then the 150th term of AP is<\/a><\/p>\n
Prove that the sum of first n natural numbers is \\(n(n+1)\\over 2\\)<\/a><\/p>\n\n\n