a,
`\sqrt{(x-3)^2}`
`=|x-3|`
`=x-3` ( vì `x>=3 \ <=> \ x-3>=0` )
b,
`\sqrt{(1-2x)^2}`
`=|1-2x|`
`=-(1-2x)` ( vì `x>=1/2 \ <=> \ 2x>=1 \ <=> \ 1-2x<=0` )
`=2x-1`
c,
`5\sqrt{(x-12)^2}`
`=5.|x-12|`
`=5.[-(x-12)]` ( vì `x<12 \ <=> \ x-12<0` )
`=5(12-x)`
`=60-5x`
d,
`2\sqrt{x^2}-5x`
`=2.|x|-5x`
`=2.(-x)-5x` ( vì `x<0` )
`=-2x-5x`
`=-7x`
e,
`\sqrt{x^2(x+1)^2}`
`=\sqrt{x^2} . \sqrt{(x+1)^2}`
`=|x| . |x+1|`
`=x(x+1)` ( vì `x>0 \ <=> \ x+1>=1>0` )
`=x^2+x`
