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x la a doua- y la a doua=16 si x+y=8, calculați 2x-2y

Răspuns :

[tex]x + y = 8[/tex]

[tex] {x}^{2} - {y}^{2} = 16[/tex]

[tex] {x}^{2} - {y}^{2} = (x -y )(x + y)[/tex]

[tex](x - y)(x + y) = 16[/tex]

[tex](x - y) \times 8 = 16 \: | \div 8[/tex]

[tex]x - y = 2 \: | \times 2[/tex]

[tex]2x - 2y = 4[/tex]