Find the Sum
By Wulfric
@Wulfric (160)
India
1 response
@srini_the_creator (196)
• India
26 Jun 07
3/13 + 33/13^2 + 333/13^3 + ...... till infinity
= 3[ 1/13 + 11/13^2 + 111/13^3 + ....till infinity ]
= 3[ 1/13 + (1+10)/13^2 + (1+100)/13^3 + .....]
= 3[ 1/13 + {1/13^2 + 10/13^2} + {1/13^3 + 100/13^3} +........infinity]
= 3[ 1/13 + 1/13^2 + 10/13^2 + 1/13^3 + 100/13^3 +.]
= 3[{1/13 + 1/13^2 + 1/13^3 +....} + { 10/13^2 + 100/13^3 =....}]
Now we can split into sun of two expressions as :
ONE : 3{1/13 + 1/13^2 + 1/13^3 +...... infinity}
SECOND : 3{10/13^2 + 100/13^3 + 1000/13^4 +.... infi}
Solutions are :
for ONE : 3[(1/13)/{1-1/13}}] Formula for G.P.
3[(1/13)/(12/13)] for infinite series
3[1/12]
1/4
for SECOND : 3[10/13^2 + 100/13^3 + ....]
Multiply with 10 and divide with 10
= (3/10)[100/13^2 + 1000/13^3 + ...]
= (3/10)[10^2/13^2 + 10^3/13^3+....]
adding 10/13 and substracting 10/13 in []
= (3/10)[10/13 + 10^2/13^2 + 10^3/13^3 +.... -10/13]
applying infinite series formula
= (3/10)[(10/13)/{1-10/13} - (10/13)]
= (3/10)[(10/13)/(3/13) - (10/13)]
= (3/10)[10/3 - 10/13]
= 3[1/3 - 1/13]
= 3[10/39]
= 10/13
Now add the results of ONE and SECOND
1/4 + 10/13
= 53/52
So the series is resulted to the value : 53/52
Please respond for the correctness of my answer
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