Question

show that a1,a2, an from an A.P if an=3+4n for 10th standard​

Answer 1

Step-by-step explanation:

Given that, nth term of the series is an = 3 - 4n For a1, Put n = 1 so a1 = 3 - 4(1) = - 1 For a2, Put n = 2, so a1 = 3 - 4(2) = - 5 For a1, Put n = 3 so a1 = 3 - 4(3) = - 9 For a1, Put n = 4 so a1 = 3 - 4(4) = - 13 So AP is - 1, - 5, - 9, - 13, … a2 - a1 = - 5 - (- 1) = - 4 a3 - a2 = - 9 - (- 5) = - 4 a4 - a3 = - 13 - (- 9) = - 4 Since, the each successive term of the series has the same difference. So, it forms an AP with common difference, d = - 4 We know that, sum of n terms of an AP is Where a = first term d = common difference and n = no of terms = 10[ - 2 - 76] = - 780 So Sum of first 20 terms of this AP is - 780.Read more on Sarthaks.com - https://www.sarthaks.com/881058/if-an-3-4n-then-show-that-a1-a2-a3-from-an-ap-also-find-s20