Question

初一数学计算题求助~急需~3.若x^2 +ax-1可分解成(x-2)(x+b),求a+b的值 4.已知a+b=-2,ab

Answer 1

3.

(x-2)(x+b)

=x^2 +(b-2)x-2b

所以 b-2=a,-1=-2b

a=- 3/2

b=1/2

a+b=-1

4.

a(a+b)(a-b)-a(a+b)^2

=a(a^2-b^2)-a(a+b)^2

=a[(a^2-b^2)-(a+b)^2]

=a[a^2-b^2-a^2-b^2-2ab]

=-2a(b^2+ab)

=-2ab(a+b)

=-10