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daca se cunoaste12+3a+6b=51 afla a+2b b stiind ca 4a+6b-3=11 afla 6a+9b c stiind ca 7a+9b+5=a+b+17 afla 15a+20b

Răspuns :

12+3a+6b=51
3a+6b=51-12=39 /3            => a+2b=13

4a+6b-3=11
4a+6b=11+3=14 /2              =>2a+3b=7    x3      =>6a+9b=21

7a+9b+5=a+b+17  => 7a-a+9b-b=17-5
6a+8b=12  /2      =>3a+4b=6      x5  => 15a+20b=30
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