Prove that    is an irrational number.   from Mathematics R

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 Multiple Choice QuestionsShort Answer Type

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105.

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109. Express 0.737373.......in the form  straight P over straight q
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110.

Prove that   open parentheses 5 minus 2 square root of 3 close parentheses is an irrational number.  


Let us assume, to the contrary, that   open parentheses 5 minus 2 square root of 3 close parentheses is rational i.e. we can find coprimes a and b (b ≠ 0) such that

5 minus 2 square root of 3 equals straight a over straight b rightwards double arrow 2 square root of 3 equals 5 minus straight a over straight b equals fraction numerator 5 straight b minus straight a over denominator straight b end fraction
rightwards double arrow space space square root of 3 equals fraction numerator 5 straight b minus straight a over denominator 2 straight b end fraction

Since a and b are integers, we get

fraction numerator 5 straight b minus straight a over denominator 2 straight b end fraction is rational, and so space space square root of 3 space is rational
BUt thisc contradicts the fact that square root of 3  
is irrational.

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#6 {main}</pre>  is an rational.

Hence, we conclude that  open parentheses 5 minus 2 square root of 3 close parentheses is an irrational number.

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