a)

$0,\underline{123}123123123123123123\dots =0,\left(123\right)$  

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b)

$1,\underline{300}300300300300300300\dots =1,\left(300\right)$    

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c)

$7,7\underline{54}545454545454545454\dots =7,7\left(54\right)$  

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d)

$5,0\underline{5678}5678567856785678\dots =5,0\left(5678\right)$  

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e)

$15,15151\underline{5}555555555555\dots =15,15151\left(5\right)$  

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f)

$0,127\underline{354}354354354354354\dots =0,127\left(354\right)$