Question

已知x大于0小于1,则4/x+9/(1-x)的最小值,且此时X=

Answer 1

[4/x+9/(1-x)]

=[x+(1-x)]*[4/x+9/(1-x)]

=4+9+4(1-x)/x+9x/(1-x)

≥13+2*√[4(1-x)/x * 9x/(1-x)]

=13+2*6

=25

则：最小值=25

此时X=1/2