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calculati : x+y=? ; xysupra liniat + yx supraliniat = patrat perfect

Răspuns :

xy +yx = patrat perf.
10x +y +10y +x=patrat perf.
11x +11y=patrat perf.
11(x+y)=patrat perf.
x+y=11^2
x+y= 121