find S30 of the series 7+77+777+.........
Answers
Answered by
1
S30 = 7+77+777+ ....+ 30 terms
= 7[1+11+111+...+30 terms]
= 7/9[9+99+999+...+ 30 terms]
=7/9 [(10-1)+(100-1)+(1000-1) + ...+ 30 terms]
= 7/9 [ (10+100+1000+ ...+30 terms) - (1+1+1+,....+30 terms)]
= 7/9[10(10^30 -1)/ (10-1) - 30] since 10 +100+1000 +.. is in GP
=7/9 [10/9(10^30 -1) -30]
=70/81(10^30-1)-70/9
= 7[1+11+111+...+30 terms]
= 7/9[9+99+999+...+ 30 terms]
=7/9 [(10-1)+(100-1)+(1000-1) + ...+ 30 terms]
= 7/9 [ (10+100+1000+ ...+30 terms) - (1+1+1+,....+30 terms)]
= 7/9[10(10^30 -1)/ (10-1) - 30] since 10 +100+1000 +.. is in GP
=7/9 [10/9(10^30 -1) -30]
=70/81(10^30-1)-70/9
hrutz:
its half solved
Answered by
1
here a is7 d is 77-7 = 70 n = 30
S30=30/2{2a+ (n-1)d}
S30 = 15{2×7 + (30-1)70}
S30= 15{14 + 29×70}
S30 = 15{14+2030}
S30 = 15×2044
S30 = 30660
S30=30/2{2a+ (n-1)d}
S30 = 15{2×7 + (30-1)70}
S30= 15{14 + 29×70}
S30 = 15{14+2030}
S30 = 15×2044
S30 = 30660
Hope it will help you. Plzzzzz mark as brainliest
thnks
this is wrong
Similar questions