5x² – 21x + 4 = 0

Go to this page to learn how to factor the left side

http://www.algebra.com/my/change_this_name32371.lesson?content_action=show_dev

5·4 = 20

20·1   20+1=21  √  
10·2   10+2=12
 5·4    5+4=9

       5x² – 21x + 4 = 0
   5x² - (20+1)x + 4 = 0
   5x² - 20x - x + 4 = 0
5x(x - 4) - 1(x - 4) = 0
     (x - 4)(5x - 1) = 0

Use the zero-factor property:

   x - 4 = 0;   5x - 1 = 0
       x = 4;       5x = 1
                     x = 

So there are two solutions, 4 and 

Edwin