x＞0
f(x)=1
xf(x)+x²＜2
x+x²-2＜0
(x-1)(x+2)＜0
x＜1
0＜x＜1
x＜0
f(x)=-1
xf(x)+x²＜2
-x+x²-2＜0
(x+1)(x-2)＜0
x+1＞0
-1＜x＜0
xf(x)+x²＜2的解集
0＜x＜1
-1＜x＜0