（x的平方-3）的平方-12（x的平方-3）+36
=(x^2-3)^2-2*(x^2-3)*6+6^2
=(x^2-3-6)^2
=(x^2-9)^2
=(x+3)^2(x-3)^2
x的平方-y的平方-x+4分之1
=x^2-x+1/4-y^2
=(x-1/2)^2-y^2
=(x-1/2+y)(x-1/2-y)
=(x+y-1/2)(x-y-1/2)
(3分之x-y）的平方-(3分之x+y）的平方
=[(x/3-y)+(x/3+y)][(x/3-y)-(x/3+y)]
=(x/3-y+x/3+y)(x/3-y-x/3-y)
=(2x/3)*(-2y)
=-4xy/3