Saved Bookmarks
| 1. |
(c) Find the sum of the first 45 terms of un AP in which the third term is 6 and the seventh termis 22. |
|
Answer» nth term = a + (n-1)d where a is a first term and d is a common difference 3rd term is 6 so a + 2d = 6 7th term is 22 so a + 6d = 22 a + 6d - a - 2d = 22 - 6 4d = 16 d = 4 a + 8 = 6 a = -2 Sn = n/2(2a+(n-1)d) S45 = 45/2 * (2*(-2) + 44*4) = 45/2 * (-4+176) = 45/2 * 172 = 45*86 = 3870 If you find this answer helpful then like it. |
|