The first term of an A.P, whose sum of n terms is given by 5n^2 - 6 is
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Answer:
Given: a
n
=5−6n
Find some of the terms of AP:
Put n=1, we get a
1
=−1= first term
Put n=2, we get a
2
=−7= second term
Common difference=d=a
2
−a
1
=−7−(−1)=−6
Sum of first n terms:
S
n
=n/2[2a+(n−1)d]
=n/2[−2+(n−1)(−6)]
=n(2−3n)
Sum of first 20 terms:
S
20
=20/2[2(−1)+(20−1)(−6)]
=10[−2−114]
=−1160
Sum of its first 20 terms of AP is −1160.
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