Giải thích các bước giải:
a) ĐKXĐ: $x \ne y,x \ne - y$
$\eqalign{ & b)\,P = \frac{{x + y}}{{2x - 2y}} - \frac{{x - y}}{{2x + 2y}} - \frac{{{y^2} + {x^2}}}{{{y^2} - {x^2}}} \cr & = \frac{{{{(x + y)}^2} - {{(x - y)}^2}}}{{2(x - y)(x + y)}} + \frac{{{y^2} + {x^2}}}{{{x^2} - {y^2}}} \cr & = \frac{{({x^2} + 2xy + {y^2}) - ({x^2} - 2xy + {y^2}) + 2({y^2} + {x^2})}}{{2(x - y)(x + y)}} \cr & = \frac{{4xy + 2{x^2} + 2{y^2}}}{{2(x - y)(x + y)}} \cr & = \frac{{{x^2} + 2xy + {y^2}}}{{(x - y)(x + y)}} \cr & = \frac{{{{(x + y)}^2}}}{{(x - y)(x + y)}} \cr & = \frac{{x + y}}{{x - y}} \cr} $
