5:-If sum of n terms of A.P.is Ax^2 + Bx find the 20th term.
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Answer:
T
n
=5n−3
T
1
=5(1)−3=2
T
2
=5(2)−3=7
d=T
2
−T
1
=7−2=5
a=T
1
=2
S
20
=
2
20
[2a+19d]
=10(4+95)
=990.
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