Identity facturization

1. 9a^2-49
= (3a)^2-7^2
= (3a+7)(3a-7)

2. 4a^7 - 7a^4 -28a^5 + a^6
= 4a^7 + a^6 -28a^5 - 7a^4
= a^6 (4a+1) - 7a^4 (4a+1)
= (a^6-7a^4) (4a+1)
= a^4(a^2-7)(4a+1)

3. a+f+af+fg+g+gt+ta+t+1
= a+af+ta+g+fg+gt+1+f+t
= a(1+f+t)+g(1+f+t)+(1+f+t)
= (a+g+1)(1+f+t)