1) (t^2-4) \ (2t+4)= (t-2)(t+2) \ (2(t+2) ) = (t-2) \ 2
2) (25-x^2)\(2x+10)=(5-x)(5+x)\(2*(x+5))=(5-x)\2
3) (6xm+18m)\(9-x^2)=6m(x+3)\((3-x)*(3+x))=6m\(3-x)
4) (3x^2-15xy)\(x^2-25^y^2)=3x(x-5y)\((x-5y)*(x+5y))=3x\(x+5y)
5) (a^3-16a)\(a^2+4a)=a*(a-4)(a+4)\ (a*(a+4))=a-4
6) (t^2-9t)\(81t-t^3)=t(t-9)\(t*(9-t)*(9+t))=-1\(9+t)