vrfdt84h
花朵
共回答了22个问题采纳率:100% 举报
证明:设在负无穷到正无穷上有x,y
且 x0
若x,y异号
y^(2/3)+y^(1/3)x^(1/3)+x^(2/3)
=[y^(1/3)+x^(1/3)]^2-y^(1/3)x^(1/3)>0
若x,y同号
y^(2/3)+y^(1/3)x^(1/3)+x^(2/3)
=[y^(1/3)-x^(1/3)]^2+3y^(1/3)x^(1/3)>0
所以f(y)-f(x)>0
故f(x)=x的开三次方在R上单调递增.
1年前
10