已知m^2-mn=21,mn-n^2=-15,求代数式:(1)m^2-n^2 (2)m^2-2mn+n^2

问题描述:

已知m^2-mn=21,mn-n^2=-15,求代数式:
(1)m^2-n^2 (2)m^2-2mn+n^2