A)=8-(6a+8-3a^2+4a)=8-6a-8+3a^2-4a=3a^2-10a;
b)=2a^3+(5a+5a^2-2a^2-2a^3)=3a^2+5a;
c)=2-2x+2x-2x^2 +(2-x-4x+2x^2)=2-2x+2x-2x^2+2-5x+2x^2=-5x+4
3x-π/7=π/2+πn 3x=π/2+π/7+πn=π(1/2+1/7)+πn=9π/14+πn
x=3π/14+πn/3
У=-5х-6
у=-6
-5х-6=-6
-5х=-6+6
-5х=0|÷(-5)
х=0