a(-2)？ +b(-2)=m[a(- 1)？ +b(- 1)]+n[a+b], simplified.

4a-2b=m[a-b]+n[a+b]

4a-2b=(m+n)a-(m-n)b

So: m+n=4, m-n=2, solve the equations simultaneously.

m=3，n= 1

Therefore, f(-2)=3f(- 1)+f( 1) is obtained from the known conditions.

-3≤3f(- 1)≤6，2≤f( 1)≤4

The sum of the two formulas gives-1≤ 3f (-1)+f (1) ≤10, that is

- 1≤f(-2)≤ 10

Multiply 2 by f(x)>k to get 2x/(x? +6)>； K, the denominator is x? +6, greater than 0, multiplied by x on both sides of the inequality? +6, the sign of inequality invariants, namely 2x >；; k(x？ +6), complete

kx？ -2x+6k & lt； 0

According to the meaning of the question, the solution of the above inequality is x < -3 or x & gt-2, so we know

Equation kx? The root of -2x+6k=0 is x= -3 or x= -2, so it is obtained by Vieta theorem.

(-3)+(-2)=2/k, and the solution is obtained.

k= -2/5

3. Let's buy X-rays at 80 cents and Y-rays from 2 yuan, depending on the meaning of the question.

0.8x+2y≤ 10 (x≥2，y≥2)

When y=2, x=2, 3, 4, 5, 6, 7 (6 kinds)

When y=3, x=2, 3, 4, 5 (4 kinds)

When y=4, x=2 (1 species)

1* *11species