Solution: a 2+b 2-4a-6b+ 13 = 0.

Divide 13 into 4 and 9.

(a^2-4a+4)+(b^2-6b+9)=0

(a-2)^2+(b-3)^2=0

a-2=0，= = & gta=2

b-3=0，= = & gtb=3

a+b=2+3=5

Two: 2 (a-3) 2-a+3

Solution:

2(a-3)^2-a+3

=2(a-3)^2-(a-3)

= (a-3)(2a-6- 1)

=(a-3)(2a-7)

3: If x is an arbitrary rational number, the value of the polynomial x-1-(1/4 * x 2) (d).

A: It must be negative B: It can't be positive C: It must be positive D: It's all rational numbers.

Solution: 1/4 * x 2 equals x 2/4 = (x/2) 2.

(x/2)^2-x- 1

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

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

=(x/2- 1)^2-2

Because (x/2-1) 2 >; 0

So (x/2- 1) 2-2 has both positive and negative numbers.

Option d