已知m=X方-Y方分之2XY,N=X方-Y方分之X方+Y方求M-N化简求值其中X:Y=5:2

题目

已知m=X方-Y方分之2XY,N=X方-Y方分之X方+Y方求M-N化简求值其中X:Y=5:2

答案

M-N=2xy/(x^2-y^2)-(x^2+y^2)/(x^2-y^2)
=[2xy-(x^2+y^2)]/(x^2-y^2)
=-(x-y)^2/[(x+y)(x-y)]
=(y-x)/(x+y)
=-7/3