CBSE Class 10 Answered
if s7=36 and s8=25 then a8=
Asked by kallutlabhagya123 | 14 Oct, 2020, 11:36: AM
It is assumed that this question is related to arithmetic progression. S7 means sum of first seven terms in arithmatic progression.
Similarly a8 means eighth term in arithmetic progression.
7 terms gives sum as 36 .
If eigth term is added to above sum, we get sum of 8 terms as 25.
Hence added eigth term = 36-25 = 11
Though above calculation is straight forward, we should know how to calculate a particular term in arithmetic progression
by knowing sum of m terms and sum of n terms , were m and n can be any number.
Following method of finding calculation is used for this.
Sum of n-terms = Sn = (n/2) [ 2a + (n-1)d ]
S7 = ( 7/2) [ 2a + 6d ] = 36 or 2a + 6d = 72/7 ................... (1)
S8 = ( 8/2) [ 2a + 7d ] = 25 or 2a + 7d = 25/4 ..................(2)
Hence eqn.(2) - eqn.(1) gives , d = (25/4) - (72/7) = -113/28
by substituting d in eqn.(1), we get a = 17.25
Eighth term = a + 7d = 17.25 - [ 7 × 113/28 ] = -11
Answered by Thiyagarajan K | 14 Oct, 2020, 21:04: PM
Application Videos
Concept Videos
CBSE 10 - Maths
Asked by dheerrana109 | 22 Jul, 2024, 10:26: AM
CBSE 10 - Maths
Asked by vishwanathhikkalagutti | 17 Jul, 2024, 07:25: AM
CBSE 10 - Maths
Asked by avadheshkumar94 | 13 Jul, 2024, 20:18: PM
CBSE 10 - Maths
Asked by 3ra2231 | 11 Jul, 2024, 20:55: PM
CBSE 10 - Maths
Asked by avadheshkumar94 | 10 Jul, 2024, 10:14: AM
CBSE 10 - Maths
Asked by syashkurun | 08 Jul, 2024, 19:14: PM
CBSE 10 - Maths
Asked by francissaka528 | 08 Jul, 2024, 06:15: AM
CBSE 10 - Maths
Asked by radhe9868017031 | 05 Jul, 2024, 14:10: PM
CBSE 10 - Maths
Asked by naidulokesh892 | 04 Jul, 2024, 20:42: PM