Răspuns:
1) 2x+y=7 => y= 7-2x si inlocuim pe y in prima ec
x+5*(7-2x)= 8 x+35-10x=8 35-9x=8 9x=35-8=27
x= 27:9 =3 x=3 y=7-2*3= 7-6=1 y=1
3) [tex]\left \{ {{3x+7y=5} \atop {2x-4y=-9}} \right.[/tex] inmultim cu 4 prima ec si cu 7 a doua ec
[tex]\left \{ {{12x+28y=20} \atop {14x-28y=-63}} \right.[/tex] => 2x=43 x=43/2
inlocuim pe x in a 2 ec y=(2*43:2 +9):4= ( 43+9):4=52:4=13
y=13
2) adunam ec => 2x[tex]\sqrt{2}[/tex] -x[tex]\sqrt{2}[/tex]=2 => x[tex]\sqrt{2}[/tex] = 2 => x=2/ [tex]\sqrt{2}[/tex]
x= [tex]\sqrt{2}[/tex] *[tex]\sqrt{2}[/tex] : [tex]\sqrt{2}[/tex] = [tex]\sqrt{2}[/tex] x=[tex]\sqrt{2}[/tex] inlocuim intr-o ecuatie sa aflam y
-[tex]\sqrt{2}[/tex] *[tex]\sqrt{2}[/tex] -y=1 => y= -2-1= -3 y=-3
4) sistem imposibil deoarece daca le scadem se reduce si x si y
