1.

Find the sum of the following series:`(sqrt(2)-1)+1+(sqrt(2)-1)+oo`

Answer» We have
`1/((sqrt(2)+1))=1/((sqrt(2)+1))xx((sqrt(2)-1))/((sqrt(2)-1))=((sqrt(2)-1))/1`.
So, the given series is an infinite geometric series in which `a=(sqrt(2)+1)` and `r=(sqrt(2)-1) lt 1`.
Hence, the sum of the given infinite geometric series is
`S=a/((1-r))=((sqrt(2)+1))/({1-(sqrt(2)-1)})=((sqrt(2)+1))/((2-sqrt(2)))xx((2+sqrt(2)))/((2+sqrt(2)))`
`=(4+3sqrt(2))/((4-2))=((4+3sqrt(2)))/2`.


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