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Determinati x3+9y+11 stiind ca x+3y=10

Răspuns :

dam factor comun pe:3
3(x+3y) +11=3x10+11=30+11=41
x3+9y+11
dam factor comun 3:
3(x+3y)+11=?  dar x+3y=10
deci  3×10+11=30+11=41
deci 
x3+9y+11=41