379.a) . 6x²-(7x²-x)=6x²-7x²+x=-x²+x=-x(x-1);
x=0,1;⇒-x(x-1)=-0,1(0,1-1)=(-0,1)·(-0,9)=0,09;
б). -(12x-1)+(9x+4)=-12x+1+9x+4=-3x+5;
x=11.2;⇒-3x+5=-3·11.2+5=-33.6+5=-28.6
в). (a²-a)-(3a+a²)=a²-a-3a-a²=-4a;
a=9.21;⇒-4a=-4·9.21=-36.84;
г). -(c³-1)+(c³+c-1)=-c³+1+c³+c-1=c;
c=12.718