The sum of the 5th and the 9th term of an AP is 30. If its 25tb term is three times its 8th term, find the AP
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Answer:
a = 3 , d = 2, A.P = 3,5,7,9,...
Step-by-step explanation:
Nth term in an A.P = a+(n-1)d
5th term = a+(5-1)d = a+(4)d
9th term = a+(9-1)d = a+(8)d
= a+(4)d + a+(8)d = 30
= 2a+12d =30
= a+6d = 15
= a = 15-6d
7th term = 15
25th term = 3(8th term)
a+(25-1)d = 3[a+(8-1)d]
a+24d = 3a+21d
24d-21d = 3a-a
3d = 2a
3d = 2(15-6d)
3d = 30 -12d
15d = 30
d = 2
a = 15 - 6(2)
a = 15-12 =3
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