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a) daca 2a-3b=15 si a-b=4, calculati 3a-4b


Răspuns :

2a-3b=15

a-b=4=>a=4+b

2(4+b)-3b=15

8+2b-3b=15

8-b=15=> -b=7=>b= -7

a=4-7=-3

3a-4b= 3*(-3)-4*(-7)= -9+28=19