В приложении.....................
m(m-7)-(m-3)(3+m)
m^2-7m-(3m+m^2-9-3m)
m^2-7m-(m^2-9)
m^2-7m-m^2+9
-7m+9, при m= -3,
-3*(-7)=21+9=30.
3x(x+y+c)-3y(x-y-c)-3c(x+y-c)=3x^2+3xy+3xc-3xy+3y^2+3yc-3cx+3cy+3c^2=