Y=X+√(X^2+1)Y的定义域是实数设X1>X2有Y1=X1+√(X1^2+1),Y2=X2+√(X2^2+1)而Y1-Y2=X1-X2+√(X1^2+1)-√(X2^2+1)=X1-X2+(√(X1^2+1)+√(X2^2+1))/(X1^2-X2^2)因为X1>X2,==>X1-X2>0 X1^2-X2^2>0 而且(√(X1^2+1)+√(X...