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calculati 5x + 7y +2x ca x+y 123 si y+z 257

Răspuns :

x+y=123 /x5
5x+5y=615

y+z 257 /x2
2y+2z=514

Adunam
5x+5y+2y+2z=615+514
5x+7y+2z=1129
5x + 7y +2 z=1129
 x+y =123 si y+z= 257
il descompun pe 7y=5y+2y
5x + 7y +2 z = 5x+5y+2y+2z=
=5(x+y)+2(y+z)=5x123+2x257=615+514=1129