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Stiind ca:x+y=5150; y+z=11888
afla:x+3xy+2xz


Răspuns :

x+3xy+2xz=x+x(3y+2z)

x+y=5150
y+z=11888 inmultim cu 2

x+y=5150
2y+2z=23776

adunam relatiile
x+y+2y+2z=5150+23776
x+3y+2z=28926
deci 3y+2z=28926-x

inlocuim in prima relatie
x+3xy+2xz=x+x(3y+2z)=x+x(28926-x)=
x+28926x-x^2=28927x-x^2

unde x^2 - x la puterea a doua