Question

1.已知4x^2+7x+2=4,求-12x^2-21x的值

Answer 1

1.已知4x^2+7x+2=4,求-12x^2-21x的值

4x^2+7x+2=4

4x^2+7x=2

-12x^2-21x

=-3(x^2+7x)

=-3*2

=-6

2.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)-12x+k

=x^2(2x+1)-x(2x+1)-6(2x+1)

k=-6