# Find the sum of first n terms of the series. 7+77+777+.......

2
by Deleted account

2014-05-08T08:14:35+05:30

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7, 77, 777, 7777 ….to n terms.
Sn=7+77+777+7777+……+to n terms
introducing 9
= (7/9) [9+99+999+……+ to n terms]
= (7/9) [(10-1) + (100-1) + (1000-1) +……...+ to n term]
= (7/9) [10+100+1000+……... n terms – (1+1+1+1+…… n terms)
= (7/9) [10+100+1000+………n terms –n]
Here      a=10, r=10
= (7/9) [10(10n-1)/ (9) - n]
Thanx limzy
u r always welcme Shruthi
2014-05-09T22:43:33+05:30

### This Is a Certified Answer

Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
Sn=7+77+777+7777+……+to n terms
= (7/9) [9+99+999+……+ to n terms]
= (7/9) [(10-1) + (100-1) + (1000-1) +……...+ to n term]
= (7/9) [10+100+1000+……... n terms – (1+1+1+1+…… n terms)
= (7/9) [10+100+1000+………n terms –n]
a=10, r=10
= (7/9) [10(10 n-1)/ (9) - n]
Thanx shanju
THANK YOU FRND!!!!!!!!!!!!