`a)` `M=(xsqrty +ysqrtx)/(x+2sqrt{xy}+y)` `(x,yge0;xyne0)`
`=(sqrt{xy}(sqrtx +sqrty))/((sqrtx)^2+2*sqrtx*sqrty+(sqrty)^2)`
`=(sqrt{xy}(sqrtx +sqrty))/(sqrtx+sqrty)^2`
`=sqrt{xy}/(sqrtx+sqrty)`
Vậy với `(x,yge0;xyne0)` thì `M=sqrt{xy}/(sqrtx+sqrty)`
`b)` `N=(3sqrta -2a -1)/(4a-4sqrta+1)` `(age0;ane1/4)`
`=(-2a +3sqrta -1)/(4a-4sqrta+1)`
`=(-2a+2sqrta+sqrta-1)/((2sqrta)^2-2*2sqrta*1+(1)^2)`
`=(-2sqrta(sqrta-1))+(sqrta-1))/(2sqrta-1)^2`
`=(-(2sqrta-1)(sqrta-1))/(2sqrta-1)^2`
`=-(sqrta-1)/(2sqrta-1)`
Vậy với `(age0;ane1/4)` thì `N=-(sqrta-1)/(2sqrta-1)`
