172.
1) =3a²b (16a⁴ -81b³)
2) = (a+1)(a+2)-(a+1)(a-2)-(a+1)=
=(a+1)(a+2-(a-2)-1)=(a+1)(a+2-a+2-1)=3(a+1)
3) =(x²y² -y²t²)+(x²z²-z²t²)=y²(x²-t²)+z²(x²-t²)=
=(x²-t²)(y²+z²)=(x-t)(x+t)(y²+z²)
4) = (a-b)(a+b)(a-c)-(a-c)(a+c)(a+b)=
=(a+b)(a-c)(a-b-(a+c))=(a+b)(a-c)(a-b-a-c)=
=(a+b)(a-c)(-b-c)=-(a+b)(a-c)(b+c)=(a+b)(c-a)(b+c)
5) =(x+2y+3y)(x+2y-3y)=(x+5y)(x-y)