1) (m-n)^2 - (m+n)^2 (m-n-m-n)(m-n+m+n) -2n*2m 4mn
----------------------- = -------------------------- = ------------- = ------------
(m+n)(m-n) m^2 - n^2 m^2 - n^2 n^2 - m^2
2) x-1-x+3 2 2
----------- = ------------------- = ---------------
(x-3)(x-1) x^2 - x - 3x + 3 x^2 - 4x + 3
3) (2a+3b)^2 + (2a-3b)(2a-b) 4a^2+12ab+9b^2+4a^2-2ab-6ab+3b^2
--------------------------------- = ---------------------------------------------- =
(2a+3b)(2a-3b) 4a^2-9b^2
8a^2+4ab+12b^2
= -----------------------
4a^2-9b^2