A=2*0+m=m, b=2m+m=3m [a, b] The length is b-a=2m.

The length of [0, m] is: m from the meaning of the question: 2m-m = 5-> m=5.

2、f(x)+2f(-x)=3x+x^2 ①

f(-x)+2f(x)=3(-x)+(-x)^2=-3x+x^2②

f(x)=(②*2-①)/3=-3x+( 1/3)x^2

3. Decomposition of constant term with quadratic coefficient 1 -(a+2)

1 a+2

1 - 1

If the result of diagonal multiplication and addition is a linear coefficient (a+ 1), the decomposition is correct.

The factorization is: [x-(a+2)][x-(- 1)].