`#Mon`
`a)P=\frac{\sqrt{a}(1-a)^2}{1+a}:[(\frac{1-\sqrt{a^3}}{1-\sqrt{a}}+\sqrt{a})(\frac{1+\sqrt{a^3}}{1-\sqrt{a}}-\sqrt{a})]`
`=\frac{\sqrt{a}(1-a)^2}{1+a}:[(\frac{(1+\sqrt{a})(1+\sqrt{a}+1)}{1-\sqrt{a}}+\sqrt{a})(\frac{(1+\sqrt{a})(1-\sqrt{a}+1)}{1+sqrt{a}}-\sqrt{a})]`
`=\frac{\sqrt{a}(1-a)^2}{1+a}:[(a+2\sqrt{a}+1)(a-2\sqrt{a}+1)]`
`=\frac{\sqrt{a}(1-a)^2}{1+a}:[(\sqrt{a}+1)^2(\sqrt{a}-1)^2]`
`=\frac{\sqrt{a}(1-a)^2}{1+a}:(a-1)^2`
`=\frac{\sqrt{a}}{1+a}`
`b)M=a.(\frac{\sqrt{a}}{1+a}-\frac{1}{2})`
`=a.\frac{2\sqrt{a}-a-1}{2(1+a)`
`=-a.\frac{(\sqrt{a}-1)^2}{2(a+1)}`
`Vì` `\frac{a(\sqrt{a}-1)^2}{2(a+1)}>0`
`=>M<0`
