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a×b=420
(a+5)×(b-2)=400


Răspuns :

a×b=420
(a+5)(b-2)=400
ab+5b-2a-10=400
420+5b-2a-10=400
2a-5b=10
b=420/a
2a-5*420/a=10
2a²-2100=10a
a²-5a-1050=0
a²+30a-35a-1050=0
a(a+30)-35(a+30)=0
(a+30)(a-35)=0
a=35
b=420:35=12

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