1. Find the sum of the sequence 7,77,777,7777,......to n terms. Please give a detailed explanation

1. Find the sum of the sequence 7,77,777,7777,......to n terms. Please

1.	1. Find the sum of the sequence 7,77,777,7777,......to n terms. Please give a detailed explanation
Answer» 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] \xa0Here a=10, r=10 \xa0= (7/9) [10(10n-1)/ (9) - n]