Factor
1. a^4-16
2. (m-n)^2-(2m+3n)^2
3.2x^4y^4-6x^5y^3+8x^3y
4.12m^2n^3+18m^3n^2
1. and 2. --- difference of squares
3. and 4. --- take out highest common factor and go from there
1. a^4-16
2. (m-n)^2-(2m+3n)^2
3.2x^4y^4-6x^5y^3+8x^3y
4.12m^2n^3+18m^3n^2
3. and 4. --- take out highest common factor and go from there