Răspuns:
Explicație pas cu pas:
4*0,(4) = 4*4/9 = 16/9
√16/9 = 4/3
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40*0,0(4) = 40*4/90 = 16/9
√16/9 = 4/3
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400*0,00(4) = 400*4/900 = 16/9
√16/9 = 4/3
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4/3 + 4/3 + 4/3 = 12/3 = 4
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x = 25*4 = 100 = 10^2, patrat perfect