Calculate the sum of the series 5 + 55 + 555 + ……..+ n
a.(10n – 1) – (5/9)n
b.50/81(10n – 1) – (5/9)n
c.50/81(10n – 1) – (5/9)
d.(10n – 1) – (5/9)5n
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sum of n terms = n/2 [ 2 a + { n-1} d ]
FROM GIVEN QUESTION ::
a = 5 ,d = 55 - 5 = 50
on solving ::
= n/2 [2 * 5 +{n -1 } 50 ]
= n/2 [ 10+ {n-1} 50]
= 5 n + n/2 { 50 n - 50}
= 5n + 25n ^2 - 25n
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