# :(impossible factoring questions

#### stuckonmath

Hi everyone! I have about 200 problems on factoring, all due tmrw ! I'm really stuck on a few of these, and if you could help me that would be great!

12m^3 y - 75my^3

10x^3 y + 21x^2 y^2 + 9xy^3

2a^3 b +11a^2 b^2 - 21ab^3

6x^3 y + 7x^2 y^2 - 20xy^3

2x^4 -512

243 - 3y^4

625m^4 - 16

Thanks so much!

#### tonio

Hi everyone! I have about 200 problems on factoring, all due tmrw ! I'm really stuck on a few of these, and if you could help me that would be great!

12m^3 y - 75my^3

10x^3 y + 21x^2 y^2 + 9xy^3

2a^3 b +11a^2 b^2 - 21ab^3

6x^3 y + 7x^2 y^2 - 20xy^3

2x^4 -512

243 - 3y^4

625m^4 - 16

Thanks so much!

I'll do one to give you a lead. You do the other ones:

$$\displaystyle 12m^3 y - 75my^3=3my(4m^2-25y^2)=3my(2m-5y)(2m+5y)$$

So first you factor out a common factor ( $$\displaystyle 3my$$ ) , and then you use the formula for squares difference $$\displaystyle a^2-b^2=(a-b)(a+b)$$ , with $$\displaystyle a=2m\,,\,\,b=5y$$

Tonio