>>769
ｚ＝{（ｘ＋1)^2＋y^2}/(x＋１）y
=(x+1)/y + y/(x+1)
≧2√{(x+1)/y * y/(x+1)}
=2
等号は (x+1)/y=y/(x+1)
x=-3/5 , y=2/5