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Va rog ! a+b=5 , b+c=7 calculați 3a+5b+2c , c-a .

Răspuns :

a+b=5 I x3 =>3a+3b=15
b+c=7 I x2 =>2b+2c=14
3a+3b+2b+2c=15+14
3a+5b+2c=29
(b+c)-(a+b)=7-5
b+c-a-b=2=>c-a=2