`#Mon`
`A=\sqrt{27.48(1-a)^2}` `với` `a>1`
`=\sqrt{1296(1-a)^2}`
`=\sqrt{36^2(1-a)^2}`
`=36(1-a)`
`=36(a-1)` `\text{ ( vì a>1)}`
`B=\frac{1}{a-b}\sqrt{a^4(a-b)^2}` `với` `a>b`
`=\frac{1}{a-b}.a^2|a-b|`
`=\frac{1}{a-b}.a^2(a-b)`
`=a^2`
`C=\sqrt{5a}.\sqrt{45a}-3a` `với` `a>=0`
`=\sqrt{5a.45a}-3a`
`=\sqrt{225a^2}-3a`
`=\sqrt{15^2.a^2}.3a`
`=15|a|-3a`
`=15a-3a`
`=12a`
`D=(3-a)^2-\sqrt{0,2}.\sqrt{180a^2}` `\text{ với a tuỳ ý}`
`=(3-a)^2-\sqrt{0,2.180a^2}`
`=(3-a)^2-\sqrt{36a^2}`
`=9-6a+a^2-6|a|`
`+)Với` `a>=0` `=>D=9-6a+a^2-6a=a^2-12a+9`
`+)Với` `a<0=>D=9-6a+a^2+6a=a^2+9`
