daca a+b=203,b+c=185, atunci a+2b+c=?

Răspuns :

a + b = 203
b + c = 185
---------------- adunam cele doua relatii

a + 2b + c = 203 + 185 = 388
a + b = 203

b + c = 185 

---------------

a + 2b + c = ?

Rezolvare :

a + b = 203

c + b = 185

--------------- (+)

a + 2b + c = 203 + 185

a + 2b + c = 388 ;