Math, asked by RohitKumarSharma0000, 1 year ago

Q.1) The first and last term of an AP is 4 and 81 respectively. If the common difference is 7, how many terms are there in the AP and what is their sum?

Q.2) The sum of n terms of an AP is 5n^2-3n.Find the AP and also it's 10th term

Answers

Answered by vishal5181
0
n-12 will be the right answer hope it helps u

RohitKumarSharma0000: I need the full derivation!!!!!
Answered by GeniusShweta
3
Hey...

ur answer...


1) l=a+(n-1)d

=81=4 +7n -7

=81-4+7=7n

= 7n=84

= n=12

S10 =n/2 (a+l)

= 12/2(81+4)

=6×85

= 450


2)Sn=5n2 -3n

S(n-1)= 5(n-1)2 -3 (n-1)

=5n2 +5-10n -3n+3

= 5n2 -13n +8



n=Sn-S (n-1)

n= 5n2 -3n -5n2 +13n -8

n=10n-8


now..

S10 =10×10-8
=100-8
=92



Hope this helps u....

plz mark as brainliest answer....




GeniusShweta: plz mark as brainliest
atul103: solution is so ✌
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