36x^(2)-25. Now, we notice that 36 and 25 are squares of 6 and 5 respectively, as well as x^(2) being the square of x.
We know that (x+y)(x-y)=(x^(2)-y^(2)) or x(squared) minus y(squared)
So, we can factor the equation to be (6x+5)(6x-5) which is the same as 36x^(2)-25.
Hope this helps!