（2x+1)（-2x+1)
=(1+2x)(1-2x)
=1-4x^2
10.5x9.5
=(10+0.5)(10-0.5)
=100-0.5^2
=100-0.25
=99.75
(x-2y) (x+2y)-(x+2y)²
=(x+2y)(x-2y-(x+2y))
=(x+2y)(x-2y-x-2y)
=-4y(x+2y)
(a+b+c) (a+b-c)
=(a+b)^2-c^2
这个全部都是因式分解吗?