已知m^2-mn=20,mn-n^2=-12, 求代數式m^2-n^2與-2mn+n^2的值

已知m^2-mn=20,mn-n^2=-12, 求代數式m^2-n^2與-2mn+n^2的值

由題可知:m-n=20+mn-12-mn=8,同理以此算後一題.