determine 25th term of ap whose 9th term -6 and common difference is 5/2
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abhishek2621
31.01.2019
Math
Secondary School
+5 pts
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Find the sum of first 25 terms of ap whose nth term is given by ax = 3x +2
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Answer
4.3/5
35
Brainly User
Heya!!!
a1 = 3 ( 1 ) +2 = 5
a2 = 3 (2 ) +2 = 8
a3 = 3 ( 3 ) +2 = 11
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a25 = 3 ( 25 ) +2 = 77
5 + 8 +11 +...+ 77
It's sum is given by.
S25 = 25 / 2 [ 2 ( 5 ) + 24 × 3 ]
S25 = 1025
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Answer:
a9=a+(9-1)×d
-6=a+8×5/2
-6=a+20
a=-26
25th term=-26+(25-1)×5/2
=-26+60
=34 ans
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