Question

Rezolvați acest sistem de ecuații prin metoda substituției:
2x + y=0
x - 3y=7

Answer 1

[tex] \left \{ {{2x+y=0} \atop {x-3y=7}} \right. \Leftrightarrow \left \{ {{2x+y=0} \atop {x=3y+7}} \right. \Leftrightarrow \left \{ {{2(3y+7)+y=0} \atop {x=3y+7}} \right. \Leftrightarrow \left \{ {6y+14+y=0} \atop {x=3y+7}} \right. \Leftrightarrow \\ \\ \Leftrightarrow \left \{ {7y=-14} \atop {x=3y+7}} \right. \Leftrightarrow \left \{ {{y=-2} \atop {x=3\cdot (-2)+7}} \right. \Leftrightarrow \left \{ {{y=-2} \atop {x=1}} \right. [/tex]

Answer 2

2x + y = 0
x - 3y =7

y= -2x
x - 3y = 7

y = -2x
x - 3(-2x) = 7

y = -2x
x + 6x = 7

y = -2x
7x = 7

y = -2x
x = 1

y = -2 × 1
x = 1

y = -2
x= 1