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se stie ca: a+2b=12
b+c=10
calculate:3a+8b+2c=?


Răspuns :

a+2b = 12 /*3 => 3a + 6b = 36
b=c 10 /*2 => 2b +2c = 20 
______________________________(prin adunare rezulta)
3a + 6b + 2b +2c = 36+20
3a+8b+2c= 56
a+2b=12 I x 3
b+c=10 I x2
3a+6b=36
2b+2c=20
3a+6b+2b+2c=36+20
3a+8b+2c=56