Math, asked by krishna6567kb, 16 days ago

Find the sum of sequence 7,77,777,7777---- n terms ?

Answers

Answered by saxenadivyansh75

0

Answer:

Answer is

Step-by-step explanation:

7,77,777,7777.

.

Sn=7+77+777+7777+..to n terms

introducing 9

= 97 [9+99+999+.+ to n terms]

= 97 [(10−1)+(100−1)+(1000−1) +.+ to n term]

=97 [10+100+1000 + . n terms - (1+1+1+1+. n terms)

n terms -n ]

Here a=10,r=10

= 97 [910(10n−1)−n]

= 8170(10n−1)−n

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