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2014-04-14T13:38:35+00:00
1)
 \left \{ {{x-y=1} \atop {2x+4y=11}} \right.
 \left \{ {{x=1+y} \atop {2(1+y)+4y=11}} \right.
 \left \{ {{x=1+y} \atop {2+2y+4y=11}} \right.
 \left \{ {{x=1+y} \atop {6y=9}} \right.
y= \frac{9}{6} = 1.5,x=1+1.5=2.5
ответ: (2,5;1,5)
2)
 \left \{ {{x+y=5} \atop {x+4y=-1}} \right.
 \left \{ {{x=5-y} \atop {5-y+4y=-1}} \right.
 \left \{ {{x=5-y} \atop {3y=-6}} \right.
y= -\frac{6}{3} =-2,x=5-(-2)=7
ответ: (7;-2)
3)
 \left \{ {{x-2y=-1} \atop {4x-y=10}} \right.
 \left \{ {{x=-1+2y} \atop {4(-1+2y)-y=10}} \right.
 \left \{ {{x=-1+2y} \atop {-4+8y-y=10}} \right.
 \left \{ {{x=-1+2y} \atop {7y=14}} \right.
y= \frac{14}{2}=2,x=-1+2*2=3
ответ: (3;2)
4)
 \left \{ {{x-5y=3} \atop {-2x+3y=1}} \right.
 \left \{ {{x=3+5y} \atop {-2(3+5y)+3y=1}} \right.
 \left \{ {{x=3+5y} \atop {-6-10y+3y=1}} \right.
 \left \{ {{x=3+5y} \atop {-7y=7}} \right.
y=- \frac{7}{7}=-1,x=3+5(-1)=-2
ответ: (-2;-1)