1: 2a+2b=2(a+b)
2: 2a+4b+6c
=2*a+2*2b+2*3c
=2(a+2b+3c)
3: \(-7a-14ab-21b=-7\left(a+2ab+3b\right)\)
4: \(2ax-2ay+2a=2a\left(x-y+1\right)\)
5: \(=3a\cdot ax-3a\cdot2ay+3a\cdot4=3a\left(ax-2ay+4\right)\)
6: \(=2\cdot2ax-2\cdot ay-2\cdot1=2\cdot\left(2ax-ay-1\right)\)
7: =a^2-(2b)^2
=(a-2b)(a+2b)
8: =(5a)^2-1^2
=(5a-1)(5a+1)
9: =9(16a^2-9)
=9(4a-3)(4a+3)