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Question 1

Question 2

1.а) $\left \{ {{x+y=5,} \atop {x-y=7;}} \right. \left \{ {{2x=12,} \atop {x-y=7;}} \right. \left \{ {{x=6,} \atop {6-y=7;}} \right. \left \{ {{x=6,} \atop {y=-1}} \right.$
Ответ:(6;-1)
б) $\left \{ {{a-b=1,} \atop {a+b=-5;}} \right. \left \{ {{2a=-4,} \atop {a+b=-5;}} \left \{ {{a=-2,} \atop {-2+b=-5;}} \right. \left \{ {{a=-2,} \atop {b=-3;}} \right.$
в) $\left \{ {{2n+m=5,} \atop {2n-m=11;}} \right. \left \{ {{4n=16,} \atop {2n-m=11;}} \right. \left \{ {{n=4,} \atop {8-m=11;}} \right. \left \{ {{n=4,} \atop {m=-3;}} \right.$
2.а) $\left \{ {{u+v=4,|*5} \atop {3u-5v=20;}} \right. \left \{ {{5u+5v=20,} \atop {3u-5v=20;}} \right. \left \{ {{8u=40,} \atop {3u-5v=20;}} \right. \left \{ {{u=5,} \atop {15-5v=20;}} \right. \left \{ {{u=5,} \atop {v=-1;}} \right.$
б) $\left \{ {{3x-y=5,|*7} \atop {2x+7y=11;}} \right. \left \{ {{21x-7y=35,} \atop {2x+7y=11;}} \right. \left \{ {{23x=46,} \atop {2x+7y=11;}} \right. \left \{ {{x=2,} \atop {4+7y=11;}} \right. \left \{ {{x=2,} \atop {y=1;}} \right.$
в) $\left \{ {{4m-5n=1,} \atop {2m-3n=2;|*(-2)}} \right. \left \{ {{4m-5n=1,} \atop {-4m+6n=-4;}} \right. \left \{ {{n=-3,} \atop {2m+9=2;}} \right. \left \{ {{n=-3,} \atop {m=-3,5}} \right.$
3.а) $\left \{ {{2x+3y=-1,|*3} \atop {3x+5y=-2;|*(-2)}} \right. \left \{ {{6x+9y=-3,} \atop {-6x-10y=4;}} \right. \left \{ {{y=-1,} \atop {3x-5=-2;}} \right. \left \{ {{y=-1,} \atop {x=1;}} \right.$
б) $\left \{ {{2n-3d=-1,|*3} \atop {3n+4d=24;|*(-2)}} \right. \left \{ {{6n-9d=-3,} \atop {-6n-8d=-48;}} \right. \left \{ {{d=3,} \atop {3n+12=24;}} \right. \left \{ {{d=3,} \atop {n=4;}} \right.$
в) $\left \{ {{2a+3b=0,|*2} \atop {7a-2b=-25;|*3}} \right. \left \{ {{4a+6b=0,} \atop {21a-6b=-75;}} \right. \left \{ {{a=-3,} \atop {-21-2b=-25;}} \right. \left \{ {{a=-3,} \atop {b=2;}} \right.$