∵3-2x≥0,∴x≤3/2;
∵2x-1≥0,∴x≥1/2。
综合得函数的定义域为:[1/2,3/2].
∵y=√(3-2x)-√(2x-1)
∴dy/dx=(-1/2)*[2/√(3-2x)+2/√(2x-1)]<0,
即函数在定义域上为单调减函数,则:
ymax=f(1/2)=√(3-2*1/2)-√(1-1)=√2,
ymin=f(3/2)=√(3-3)-√(3-2*1/2)=-√2,
函数的值域为:[-√2,√2].
※.函数的凸凹性∵dy/dx
=(-1/2)*[2/√(3-2x)+2/√(2x-1)]
=-(1/2)*[2(3-2x)^(-1/2)+2(2x-1)^(-1/2)]
∴d^2y/dx^2
=(1/4)*[-2^2*(3-2x)^(-3/2)+2^2*(2x-1)^(-3/2)]
=[(2x-1)^(-3/2)-(3-2x)^(-3/2)]
令d^2y/dx^2=0,则:
(2x-1)^(-3/2)-(3-2x)^(-3/2)=0,即:
2x-1=3-2x,则:
4x=4,此时,x=1.
(1).当x∈[1/2,1)时,d^2y/dx^2>0,
此次函数y在定义上为凹函数;
(2).当x∈(1,3/2]时,d^2y/dx^2<0,
此次函数y在定义上为凸函数。
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