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Prove that x=underset(91 "times")ubrace(...

Prove that x=`underset(91 "times")ubrace(1111,....)` is composite number.

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x=`underset(91 "times")ubrace(1111,....)`
`=1+10+10^(2)+10^(3)+…+10^(90)`
`=(1(10^(91)-1))/(10-1)`
`=(((10^(13))^(7)-))/(10^(13)-1)xx((10^(13)-1))/(10-1)`
`=(1+10^(13)+10^(26)+….+10^(78))xx(1+10+10^(2)+…+10^(12))`
=Composite number
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