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a=y:4+11
b=z:5+11

a>0
b>0
y>0
z>0

ax(z:5)+bx(y:4)+11x(a+b)-2xaxb=?


Răspuns :

ax(z:5)+bx(y:4)+11x(a+b)-2xaxb=
a(b-11)+b(a-11)+11(a+b)-2ab=                      DESFACEM PARANTEZELE
=ab+ab-11a-11b+11a+11b-2ab=
=2ab-11a-11b+11a+11b-2ab=
=2ab-2ab=
=0