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daca x+2XY =15 si y-3.z=2 calculati x+3×y-3xz

Răspuns :

x+2y =15
 y-3z=2

 x+3y-3z= 
(x+2y)+(y-3z)= 15+2=17
x+2y=15
y-3z=2
x+3y-3z=(x+2y)+(y-3z)=15+2=17