9.
[tex]a) \ 12a-(5a+3)+7(2-a) =12a-5a-3+14-7a = 11\\\\b) \ 4(x-y)-3y-2(y-x)x = 4x-4y-3y-2xy+2x^{2} =2x^{2}+4x-2xy-7y\\\\c) \ 3-[2-(a+4)+2a]\cdot5 = 3-(2-a-4+2a)\cdot5 = 3-5(-2+a) = 3+10-5a=13-5a[/tex]
10.
[tex]-3x\cdot(-4y)+5x\cdot(-2xy)+2x^{2}\cdot3y = 12xy -10x^{2}y +6x^{2}y = 12xy-4x^{2}y[/tex]
11.
[tex]a) \ 3,5\cdot(a^{2}+ab-4) =3,5a^{2}+3,5ab - 14\\\\b) \ -6x\cdot(x-xy+y) = -6x^{2}+6x^{2}y - 6xy[/tex]
