(x+y)^2=x^2+y^2+2xy =25

x^2+y^2=25- 12= 13

(2)2a^2-2ab+b^2+4a+4

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

a=b a=-2 b=-2

So a 2b+ab 2 =-8-8 =- 16.

(3) A 2+(m-3) A+4 = (A+2) 2 or (A-2) 2.

So m-3=4 m=7 or m-3=-4 m=- 1.

Choose C.

(4)8a^3 b^m /(28a^n *b^n) =2b^2/

2a^3 b^m /(7 a^n*b^n) =2b^2/7

a^3 b^m/(a^n*b^n) =b^2

So n=3 m-n=2 m=5

(5)2a^2+2a+2009=2(a^2+a)+2009=2009

(6)x- 1/x = 1

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

So x 2+ 1/x 2 = 3.

Two:

( 1)-2a^3 b^2 +8a^2 b^2 -8ab^2 =-2ab^2(a^2-4a+4)=-2ab^2 *(a-2)^2

(2)a^4 -8a^2b^2 + 166^4 =？ Is it a 4-8a 2b 2+ 16b 4 = (a 2-4b 2) 2?

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

Three:

[(xy+2)(xy-2)-2x^2y^2+4] /(xy)

=[x^2 y^2 -4 -2x^2y^2+4]/(xy)

=[-x^2y^2]/(xy)

=-xy

=- 10* 1/25

=-2/5