1.已知4x^2+7x+2=4,求-12x^2-21x的值 4x^2+7x+2=44x^2+7x=2-12x^2-21x=-3(x^2+7x)=-3*2=-62.已知多项式2x^3-x^2-13x+k分解因式后有一个因式为2x+1,求k的值．2x^3-x^2-13x+k =x^2(2x+1)-2x^2-13x+k =x^2(2x+1)-x(2x+1...