the sum of first 9 terms of an arithmetic sequence is 279 and the sum of first 20 terms is 1280.find the 5 th and 16 th term ?write the sequence.
Answers
Answered by
16
Answer:
S9= (9/2) (2a+(9-1)d
=
a+4d=
a+4d=31----(i)
=10(2a+19d)=1280
2a+19d=128----(ii)
From (i) and (ii),
a +4d =31 (×2)
2a+19d=128
»2a+19d=128 (-)
2a+8d=62
=11d= 66
d= 66/11
d=6
a=31-4d
= 31-4(6)
31-24
=7
5th term
a+(n-1)d
a+5d
From eqn (i),
a+4d= 31
5th term is 31
16th term
a+15d
7+ 15(6)
7+90
=97
16 terms is 97
Sequence/AP= a,a+d, a+2d....
7,13,19,25,31,37.........
Answered by
3
Answer:
Please any one prove this equation correctly
Step-by-step explanation:
Very hard to find this
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