could someone help me with math?

Question

Factor the following trinomial completely. Look first for the greatest common factor.

20r⁴-48r³ 3-36r²

Answer 1

The greatest common factor is  4 r²  so the expression becomes

 

 4 r² (5 r² - 12 r -9)

 

The trinomial inside the parenthesis  is a medium hard case to factor.  

 There is only one way to factor 5, but two ways to factor 9.   After some experimentation

the trinomial is seen to factor as (5 r + 3) (r -3).   So the final answer is

 

   4 r² ( 5 r + 3) (r -3)