Use app×
Join Bloom Tuition
One on One Online Tuition
JEE MAIN 2025 Foundation Course
NEET 2025 Foundation Course
CLASS 12 FOUNDATION COURSE
CLASS 10 FOUNDATION COURSE
CLASS 9 FOUNDATION COURSE
CLASS 8 FOUNDATION COURSE
0 votes
15.8k views
in Arithmetic Progression by (55.4k points)
closed by

Find the sum of first 25 terms of an A.P. whose nth term is 1 - 4n.

1 Answer

+1 vote
by (44.5k points)
selected by
 
Best answer

Given: an = 1 – 4n

Taking n = 1,

a1 = 1 – 4(1) = 1 – 4 = -3

Taking n = 2,

a2 = 1 – 4(2) = 1 – 8 = -7

Taking n = 3,

a3 = 1 – 4(3) = 1 – 12 = -11

Therefore the series is -3, -7, -11, …

So, a = -3, d = a2 – a1 = -7 – (-3) = -7 + 3 = -4

Now, we have to find the sum of the first 25 terms of the AP

⇒ S25 = 25 × (-51)

⇒ S25 = -1275

Hence, the sum of 25 terms is -1275.

Welcome to Sarthaks eConnect: A unique platform where students can interact with teachers/experts/students to get solutions to their queries. Students (upto class 10+2) preparing for All Government Exams, CBSE Board Exam, ICSE Board Exam, State Board Exam, JEE (Mains+Advance) and NEET can ask questions from any subject and get quick answers by subject teachers/ experts/mentors/students.

...