20/09/28 02:34:01.35 VdFe70Zi.net
{√(1+x) - √(1+y)} / {√(1-y) - √(1-x)}
= {(1+x) - (1+y)} / {√(1+x) + √(1+y)}・{√(1-y) + √(1-x)} / {(1-y) - (1-x)}
= (x-y) / {√(1+x) + √(1+y)}・{√(1-y) + √(1-x)} / (x-y)
= {√(1-y) + √(1-x)} / {√(1+x) + √(1+y)}
= １ - (x+y)/2 + (x+y)^2 /8 - (x+y)(xx+yy) /8 + (7xx-2xy+7yy)(x+y)^2 /128 － ････
≒ １ - (x+y)/2 + (x+y)^2 /8 - (x+y)^3 /16 + 3(x+y)^4 /128 - ････
= √{(2-x-y)/(2+x+y)},