se scoate o necunoscuta dintr=o ecuatie si se introduce in cea de-a 2-a
a)4+y=0⇒y=-4
-4=-5x+1⇔5x=4+1=5⇒x=5/5=1 x=1; y=-4
b) x=7-y⇒4(7-y)-y=3⇔28-4y-y=3⇔28-3=5y⇔y=25/5=5⇔y=5
x=7-5=2 x=2 ; y=5
c)y=2x+1
6x-(2x+1)=7⇔6x-2x-1=7⇔4x=8⇔x=2
y=4+1=5 x=2; y=5
d)4y=2x+1
x+(2x+1)+2=0⇔3x=-3⇔x=-1
4y=-2+1=-1⇔y=-1/4 x=-1; y=-1/4
e)x=2-y
2(2-y)-3y=-1⇔4-2y-3y=-1⇔5=5y⇔y=1
x=1 x=1; y=1
f)x=1+y
2(1+y)+y=5⇔2+2y+y=5⇔3y=3⇔y=1
x=2 x=2;y=1