1.x^2+nxy+mxy+mny^2=x^2+(n+m)xy+mny^2=x^2+2xy-6y^2
n+m=2,mn=-6
(m+n)mn=2*(-6)=-12
2.a^2+1/a^2=3
(a-1/a)^2=a^2-2+1/a^2=3-2=1
a-1/a=1ora-1/a=-1
3.4x^2-3(a-2)x+25=0
9(a-2)^2-400=0
(a-2)^2=400/9
a-2=20/3,ora-2=-20/3
a=26/3ora=2-20/3=-14/3
4.y=x^2+6x-15=(x+3)^2-24
x=-3,ymin=-24
6.(a+b)^2-1=63
(a+b)^2=64
a+b=8or a+b=-8
7.9x^2+m+4=0
-4*9(m+4)=0
m=-4
8.(x+2)^2+(x-3)^2=13
x^2+4x+4+x^2-6x+9=13
2x^2-2x=0
x^2-x=0
x(x-1)=0
x=0,x=1
x=0時,（x+2）（3-x)=2*3=6
當x=1時,（x+2）（3-x)=3*2=6
所以（x+2)(3-x)=6