Răspuns:
Explicație pas cu pas:
{3x - y= -5
{-x + 3y = 7 I·3 =>
{3x - y= -5
{-3x + 9y = 21
------------------
8y = 16 => y = 2
x = 3y-7 => x = 3·2-7 = 6-7 => x = -1
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a) x= 1 ; y = 8 => 3·1-8 = -5 si -1+24= 23≠ 7 , solutie gresita
b) x = -4 ; y = 1 => -12+1 = -11≠ -5 ; 4+3 = 7 ; solutie gresita
c) x = -1 ; y = 2 => -3-2 = -5 ; 1+6 = 7 ; solutie corecta