The sum of 5 th and 9 th terms of an A.P.is 8 and their product is 15. Find the sum of first 28 terms of the A.P.
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Answered by
59
Answer:
a+4d+a+8d=8(given)
2a+12d=8
a+6d=4 ........(1)
(a+4d)(a+8d)=15....(2). (given)
from first a=4-6d
...(3)
put in 2
(4-2d)(4+2d)=15
16-4d^2=15
4d^2 =1
d^2=1/4
d=1/2
putting in3. , a=1
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Answered by
3
Answer:
a+4d+a+8d=8(given)
2a+12d=8
a+6d=4 ........(1)
(a+4d)(a+8d)=15....(2). (given)
from first a=4-6d
...(3)
put in 2
(4-2d)(4+2d)=15
16-4d^2=15
4d^2 =1
d^2=1/4
d=1/2
putting in3. , a=1
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