一道数学因式题目~请教高手~这部分我学的都迷糊了~

1. 3-48y^2
=3(1-16y^2)
=3(1+4y)(1-4y)

2. (x+n)^2-9
=(x+n+3)(x+n-3)

3. 49u^2-(x-y)^2
=[7u+(x-y)][7u-(x-y)]
=(7u+x-y)(7u-x+y)

平方差公式：a^2-b^2=(a+b)(a-b)

好难,成绩不过关!

主要考察平方差公式！a^2-b^2=(a+b)(a-b)

1. 3-48y^2

=3(1-16y^2)

=3(1+4y)(1-4y)

2. (x+n)^2-9

=(x+n+3)(x+n-3)

3. 49u^2-(x-y)^2

=[7u+(x-y)][7u-(x-y)]

=(7u+x-y)(7u-x+y)