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Dacă: a+b+c=198
b-c=123
atunci:

2a+b+3c=?​


Răspuns :

a+b+c = 198

b-c = 123

2a+b+3c = 2(a+b+c) - (b-c) = 2·198 - 123 = 273

Răspuns:

a+b+c=198 I·2

2a+2b+2c=396

b-c=123

(2a+2b+2c)-(b-c)=396-123

2a+2b+2c-b+c=273

2a+b+3c=273