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Daca a+b=-11 b+c=7, calculeaza a) 3a+7b+3c. B) 5a+3b-2c

Răspuns :

a=- 11-b

c=7-b

a)

[tex]3( - 11 - b) + 7b + 3(7 - b) = 0 \\ - 33 - 3b + 7b + 21 - 3b = 0 \\ - 3b + 7b - 3b = 33 - 21 \\ b = 12[/tex]

b)

[tex]5( - 11 - b) + 3b - 2(7 - b) = 0 \\ - 55 - b + 3b - 14 + 2b = 0 \\ - b + 3b + 2b = 55 + 14 \\ 4b = 69 \\ b = 17.25[/tex]