Request a call back

Join NOW to get access to exclusive study material for best results

CBSE Class 10 Answered

the sum of first n terms of an AP  5 n squared plus 3 n. if its mth term is 168,find the value of m.also find the 20th term of the AP.
Asked by amrithasai123 | 24 Feb, 2019, 12:13: PM
answered-by-expert Expert Answer
Sn = 5n2 + 3n
 
S1 = 8
 
S2 = 5×4+3×2 = 26
 
Hence in S2 terms are 8+18
 
Hence first term a  of A.P 8 and common difference d = 10
 
m-th term = tm = 8+(m-1)10 = 168 ; solving this eqn. for m, we get m = 17
 
20th term = 8+19×10 = 198
Answered by Thiyagarajan K | 24 Feb, 2019, 05:41: PM
CBSE 10 - Maths
Asked by rrajansinghakb199 | 08 Apr, 2024, 05:12: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by nagalaxmidurgarao937 | 08 Apr, 2024, 01:42: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by sonawnerohan01 | 23 Mar, 2024, 12:25: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by pathakvaishnavi9139 | 23 Mar, 2024, 10:45: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by choudharyniki001 | 22 Mar, 2024, 08:49: AM
ANSWERED BY EXPERT ANSWERED BY EXPERT
CBSE 10 - Maths
Asked by vn3950372 | 18 Mar, 2024, 08:38: PM
ANSWERED BY EXPERT ANSWERED BY EXPERT
Get Latest Study Material for Academic year 24-25 Click here
×