首先,分母 x² - xy ≠ 0,
即,x(x-y) ≠ 0, 则x≠0 且 x≠y
原式 = x(x+y)*(x-y) /[x(x-y)]
= x+y
∴原式 = x+y, 且满足 x≠0 且 x≠y