CBSE Class 10 Answered
common difference of an arithmetic progression is 3 and find a20 - a15
Asked by Kapil | 20 Oct, 2017, 09:59: AM
We know that the common difference is given as '3'.
Let 'd' be the common difference, 'a' be the first term, so the nth term is written as ![straight a subscript straight n equals straight a plus left parenthesis straight n minus 1 right parenthesis straight d](https://images.topperlearning.com/topper/tinymce/cache/5efc0051f142e68c0292fc954935024c.png)
![straight a subscript straight n equals straight a plus left parenthesis straight n minus 1 right parenthesis straight d](https://images.topperlearning.com/topper/tinymce/cache/5efc0051f142e68c0292fc954935024c.png)
We will have to find ![straight a subscript 20 minus space straight a subscript 15](https://images.topperlearning.com/topper/tinymce/cache/accba92bde8817616fab98f67a6765fe.png)
![straight a subscript 20 minus space straight a subscript 15](https://images.topperlearning.com/topper/tinymce/cache/accba92bde8817616fab98f67a6765fe.png)
Applying the formula, the above expression becomes,
(a+19d) - (a+14d)
= a + 19d - a - 14d
= 5d
This finally becomes
5 x 3
=15
Answered by | 14 Dec, 2017, 17:13: PM
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