6+11+16+21+......+71=?
Answers
Answered by
1
the answer of the sum is 539.
Answered by
0
Here a=6, d=11-6=5, an= 71
Therefore an= 71
=>a+(n-1)d=71
=>6+5n-5=71
=>1+5n=71
=> 5n= 70
=> n= 14
So, Sn= n÷2(a+an)
= 7(6+71)
= 7×77
=539
Therefore an= 71
=>a+(n-1)d=71
=>6+5n-5=71
=>1+5n=71
=> 5n= 70
=> n= 14
So, Sn= n÷2(a+an)
= 7(6+71)
= 7×77
=539
Similar questions