1)(х-2)²-4=(х-2)²-2²=(х-2+2)(х-2-2)=х(х-4)

2)(b+7)²-100c²=(b+7)²-(10c)²=(b+7+10c)(b+7-10c)

3)121-(b+7)²=11²-(b+7)²=(11+b+7)(11-b-7)=(b+18)(4-b)

4)a⁴-(7b-a²)²=(a²)²-(7b-a²)²=

=(a²+7b-a²)(a²-7b+a²)=7b(2a²-7b)

5)(4х-9)²-(2х+19)²=(4х-9+2х+19)(4х-9-2х-19)=

=(6х+10)(2х-28)

6)(a+b+c)²-(a-b-c)²=(a+b+c+a-b-c)(a+b+c-a+b+c)=

=2a(2b+2c)=4a(b+c)