Question 259221
One more step. 
Whenever you have a difference of squares, it factors as follows,
{{{z^2-a^2=(z-a)(z+a)}}}
In your case,
{{{z^2=25x^2}}}
{{{z=5x}}}
{{{a^2=1}}}
{{{a=1}}}
{{{75x^2-3=3(25x^2-1)}}}
{{{75x^2-3=3(5x-1)(5x+1)}}}