4n-m 3m+n 12mn-3m^2-12mn-4n^2 -3m^2-4n^2
--------- ---------= ---------------------------------- =------------------
20mn² - 15m²n 60m^2n^2 60m^2n^2
8 8+x^3-2x^2+2x^2-4x+4x-8 x^3
---- + x² + 2x + 4=------------------------------------------------=--------
x-2 x-2 x-2
b+3 b-1 b+3 b-1 b^2+3b-9b+9 (b-3)^2 b-3
------ ------- =-------------- - ---------------= ---------------------=----------------------=---------
9b-27 - b² - 3b 9(b-3) b(b-3) 9b(b-3) 9b(b-3) 9b