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a+b=25 si b+c=35 , calcualti 3a+6b+3c

Răspuns :

a+b=25
b+c=35 adunam cele doua relatii 
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a+2b+c=60 / *3 ⇒ 3a+6b+3c=180
a+b=25=> a=25-b
b+c=35=> c=35-b
3a+6b+3c= 3(25-b)+6b+3(35-b) =75-3b+6b+105-3b =180