f(x)=4x^3-3x
任取x1>x2>1
f(x1)-f(x2)
=4(x1^3-x^3)-3(x1-x2)
=4(x1-x2)(x1^2+x1x2+x^2)-3(x1-x2)
=(x1-x2)(4x1^2+4x1x2+4x^2-3)
=(x1-x2)[(2x1-2x2)^2+12x1x2-3]>0
单调递增
在此函数上有任意两个点(x1,y1),(x2,y2)(x1≠x2)
斜率k=(y1-y2)/(x1-x2)恒大于0
f(x)=4x^3-3x
任取x1>x2>1
f(x1)-f(x2)
=4(x1^3-x^3)-3(x1-x2)
=4(x1-x2)(x1^2+x1x2+x^2)-3(x1-x2)
=(x1-x2)(4x1^2+4x1x2+4x^2-3)
=(x1-x2)[(2x1-2x2)^2+12x1x2-3]>0
单调递增
在此函数上有任意两个点(x1,y1),(x2,y2)(x1≠x2)
斜率k=(y1-y2)/(x1-x2)恒大于0