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daca x,E R si x la 2- y la 2=408, iar x-y=12,atunic x+y este.....

Răspuns :

x²-y²=408
x-y=12
--------
(x+y)(x-y)=408
(x+y)×12=408
x+y=408:12
x+y=34

[tex]\it x-y = 12\ \ \ \ (*) \\\;\\ x^2-y^2=408\Leftrightarrow (x-y)(x+y)=408 \stackrel{(*)}{\Longleftrightarrow } 12(x+y) =408|_{:12} \Leftrightarrow \\\;\\ \Leftrightarrow x+y = 34[/tex]