[tex]b)\\\\\left \{ {{6x-(2y-3x)=7y-9} \atop {-3x+8=-2(x-2y-9)}} \right. \\\left \{ {{6x-2y+3x=7y-9} \atop {-3x+8=-2x+4y+18}} \right. \\\left \{ {{9x-9y=-9} \atop {-x-4y=10 /*9}} \right. \\+\left \{ {{9x-9y=-9} \atop {-9x-36y=90}} \right. \\-9y-36y=-9+90\\-45y=81 /:(-9)\\5y=-9 /:5\\y=-\frac95\\-x-4*(-\frac95)=10\\-x+\frac{36}5=10 /*5\\-5x+36=50\\-5x=14 /:(-5)\\x=-\frac{14}5[/tex]
[tex]c)\\\left \{ {{x-2(3-2(x-y))=23} \atop {6+5(1-3(y-x))=20x+1}} \right. \\\left \{ {{x-2(3-2x+2y)=23} \atop {6+5(1-3y+3x)=20x+1}} \right. \\\left \{ {{x-6+4x-4y=23} \atop {6+5-15y+15x=20x+1}} \right. \\+\left \{ {{5x-4y=29} \atop {-5x-15y=-10}} \right. \\-4y-15y=29-10\\-19y=19 /:(-19)\\y=-1\\\\5x-4*(-1)=29\\5x+4=29\\5x=25 /:5\\x=5[/tex]
