(a-2b)^2-(a+2b)^2=(a^2-4ab+4b^2)-(a^2+4ab+4b^2)=-8ab
(x+y)^2=x^2+2xy+y^2=3^2=9
2xy=2*2=4
x^2+y^2=9-4=5
x^2-2x+y^2+6y+10=(x^2-2x+1)+(y^2+6y+9)=(x-1)^2+(y+3)^2=0
x=1,y=-3
x-y=4
a^2-3/4a=a^2-2*3/8a
(3/8)^2=9/64
∴應(yīng)該是a^2-3/4a+9/64=(a-3/8)^2
(x-2)^(-1)=1/(x-2)
有意義即分母不為零
∴x為≠2的任意數(shù)
（m^2n+1/2mn^2）÷1/3mn=mn(m+1/2n)÷1/3mn=3m+3/2n
（a+b+c）(b-a-c)
=(b+(a+c))*(b-(a+c))
=b^2-(a+c)^2
=b^2-a^2-2ac-c^2