Answer? +b？ -2a-4b+8

=a？ -2a+b？ -4b+8

=a？ -2a+ 1+b？ -4b+4+3

=(a- 1)？ +(b-2)？ +3

Because (a- 1)? ≥0 (b-2)？ ≥0

So (a- 1)? +(b-2)？ +3≥3

2.

Because x > 5, so x-5 > 0, then | x-5 | = x-5.

① If 5 < x < 6.5, 2x- 13 < 0, then | 2x- 13 | = 13-2x.

|x-5|- |2x- 13|

=x-5- 13+2x

=3x- 18

② If x≥6.5, 2x- 13 ≥ 0, then | 2x- 13 | = 2x- 13.

|x-5|- |2x- 13|

=x-5-2x+ 13

=8-x