(2a-5b)(2a-5b-4)-12
=(2a-5b)^2-4(2a-5b)-12
=(2a-5b-6)(2a-5b+2)
(m^2*n^2+1)^2-4m^2*n^2
=(m^2*n^2+1-2m*n)(m^2*n^2+1+2m*n)
=(m*n-1)^2(m*n+1)^2
(2a-5b)(2a-5b-4)-12
=(2a-5b)^2-4(2a-5b)-12
=(2a-5b-6)(2a-5b+2)
(m^2*n^2+1)^2-4m^2*n^2
=(m^2*n^2+1-2m*n)(m^2*n^2+1+2m*n)
=(m*n-1)^2(m*n+1)^2