0

Guest

Courses New

4. How many terms of the AP. 9, 17, 25 … must be taken to give a sum of 636?

4. How many terms of the AP. 9, 17, 25 … must be taken to give a sum of 636?

Grade:12th pass

1 Answers

Pawan Prajapati
askIITians Faculty 60787 Points
2 years ago
Let there be n terms of the AP. 9, 17, 25 … For this A.P., First term, a = 9 Common difference, d = a2−a1 = 17−9 = 8 As, the sum of n terms, is; Sn = n/2 [2a+(n -1)d] 636 = n/2 [2×a+(8-1)×8] 636 = n/2 [18+(n-1)×8] 636 = n [9 +4n −4] 636 = n (4n +5) 4n2 +5n −636 = 0 4n2 +53n −48n −636 = 0 n (4n + 53)−12 (4n + 53) = 0 (4n +53)(n −12) = 0 Either 4n+53 = 0 or n−12 = 0 n = (-53/4) or n = 12 n cannot be negative or fraction, therefore, n = 12 only.

Think You Can Provide A Better Answer ?

Other Related Questions on 10 grade maths

View all Questions »

ASK QUESTION

Get your questions answered by the expert for free

Answer and earn gift vouchers

Win Gift vouchers upto Rs 500/-

View courses by askIITians

Design classes One-on-One in your own way with Top IITians/Medical Professionals

Click Here Know More

Complete Self Study Package designed by Industry Leading Experts

Click Here Know More

Live 1-1 coding classes to unleash the Creator in your Child

Click Here Know More

a Complete All-in-One Study package Fully Loaded inside a Tablet!

Click Here Know More