证明f(x)=3-2x\1+3x在(-1\3,正无穷)上是减函数

设-1/3＜X1＜X2F（X1）-F(X2)=(3-2X1) /(1+3X1) - (3-2X2)/ (1+3X2)=11(X1-X2)/(1+3X1)(1+3X2)∵（-1/3）＜X1＜X2∴(1+3X1)＞0,(1+3X2)＞0,(X1-X2)＜0∴F（X1）-F(X2) ＜0F(x)=(3-2x)/(1+3x)在(-1\3,正无穷)上是减函...