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cat face : 
( 1 supra 3) totul la a doua + ( 1 supra 3 - 1 supra noua ) totul la a doua 


Răspuns :

( 1/ 3) ² + ( 1 / 3 - 1 /9 )²=1/9-(3/9-1/9)²=1/9-(2/9)²=1/9-4/81=9/81-4/81=5/81