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a+b=16 b+c=15
5a+7b+2c=


Răspuns :

scazand primele 2 ecuatii obtinem ca a-c=1, deci a=c+1
Inlocuim "a" in ultima ecuatie:
5(c+1)+7b+2c=
7(b+c)+5=
7*15+5= 110

a+b=16
b+c=15
   
5a + 7b + 2c = 5a + 5b + 2b +2c =
 = 5(a+b) + 2(b+c) = 5 × 16 + 2 ×15 = 80 + 30 = 110