[tex]a)\\\\ 1,2x+y-(1,3x-2y)+(0,8x-2y) =1,2x+y- 1,3x+2y + 0,8x-2y =0,7x+y \\\\ x=5,\ \ y=1,8\\\\ 0,7x+y=0,7*5+1,8=3,5+1,8=4,3\\\\b)\\\\ 3x(x-2y)-2y(y-3x)=3x^2-6xy-2y^2+6xy=3x^2-2y^2\\\\x=5,\ \ \ y=-5\\\\3x^2-2y^2=3*5^2-2*(-5)^2=3*25-2*25=75-50=25[/tex]
[tex]c)\\\\ 6(x-2)-(5-2x)*(-3)=6x-12-(-15+6x)=6x-12+15-6x =3[/tex]
