1.

`3/5+4/5^2+ 3/5^3+4/5^4+ ... ` to 2n terms;

Answer» Correct Answer - `19/24.((5^(2n)-1)/5^(2n))`
Given sum `={3/5+3/5^(3)+3/5^(5)+..."to n terms"}+{4/5^(2)+4/5^(4)+..."to n terms"}`
`=(3/5xx{1-(1/5^(2))^(n)})/((1-1/5^(2)))+(4/5^(2)xx{1-(1/5^(2))^(n)})/((1-1/5^(5)))`
`=(3/5xx25/24) ((5^(2n)-1))/5^(2n)+(4/25xx25/24) ((5^(2n)-1))/5^(2n)`
`=(5/8+6/1)((5^(2n)-1)/5^(2n))=19/24.((5^(2n)-1)/5^(2n))`.


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