FIND THE SUM OF 7+77+777+7777........................upto n terms. [CBSE CLASS 11 MATHEMATICS-CHAPTER-SEQUENCES AND SERIES].
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Answered by
4
Here you go,
7+77+777+7777+............upto n terms
=7[1+11+111+1111+.............n terms]
=7/9[9+99+999+9999+...........n terms]
=7/9[(10-1)+(100-1)+(1000-1)+...........n terms]
=7/9[(10+100+1000+...........n terms)-(1+1+1+1+1+.......n terms)]
=7/9[10(10^n-1)/9-n]
Hope that helps.10+100+1000...... is in GP.
Thanks.
Tripathy
7+77+777+7777+............upto n terms
=7[1+11+111+1111+.............n terms]
=7/9[9+99+999+9999+...........n terms]
=7/9[(10-1)+(100-1)+(1000-1)+...........n terms]
=7/9[(10+100+1000+...........n terms)-(1+1+1+1+1+.......n terms)]
=7/9[10(10^n-1)/9-n]
Hope that helps.10+100+1000...... is in GP.
Thanks.
Tripathy
satichahal123:
Stupid
In the place of 7/9 their should be 7/81
Copy tumne kia ha
That's why you are shouting
Nonsense
Your answer is wrong and it will always be wrong
The answer that I have given is right
Answered by
1
Sn=7+77+777+.............n terms
=7 [1+11+111+.............n terms]
=7/9 [9+99+999+..........n terms]
=7/9 [(10-1)+(100-1)+(1000-1).......n terms]
=7/9 [10+100+1000+.......n terms] -[1+1+1+.......n terms]
=7/9 [(10 (10^n-1)/10-1)-n]
=7/81 [10 (10^n-1)-9^n]
HOPE IT'S HELPFUL...............
=7 [1+11+111+.............n terms]
=7/9 [9+99+999+..........n terms]
=7/9 [(10-1)+(100-1)+(1000-1).......n terms]
=7/9 [10+100+1000+.......n terms] -[1+1+1+.......n terms]
=7/9 [(10 (10^n-1)/10-1)-n]
=7/81 [10 (10^n-1)-9^n]
HOPE IT'S HELPFUL...............
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