f(x)=x(2x+3)
при x=-1
f(-1) = (-1)(2*(-1) + 3) = -(-2+3) = -1
f (x)=2x^2+3x; x=-1
f (x)=2*(-1)^2+3*(-1)
f (x)=2*1-3
f (x)=-1
