Đáp án+Giải thích các bước giải:
`a)\sqrt{9x^2}-2x(x<0)`
`=\sqrt{(3x)^2}-2x`
`=|3x|-2x`
`=-3x-2x(x<0)`
`=-5x`
`b)2\sqrt{x^2}(x>=0)`
`=2|x|`
`=2x(x>=0)`
`c)3\sqrt{(x-2)^2}(x<2)`
`=3|x-2|`
`=3(2-x)(x<2=>x-2<0)`
`=6-3x`
`d)2\sqrt{x^2}-5x(x<0)`
`=2|x|-5x`
`=2(-x)-5x(x<0)`
`=-7x`
`e)\sqrt{25x^2}+3x(x>=0)`
`=\sqrt{(5x)^2}+3x`
`=|5x|+3x`
`=5x+3x(x>=0)`
`=8x`
`f)\sqrt{9x^4}+3x^2(x \in RR)`
`=\sqrt{(3x^2)^2}+3x^2`
`=|3x^2|+3x^2`
`=3x^2+3x^2(3x^2>=0AAx \in RR)`
`=6x^2`
`g)x-4+\sqrt{16-8x+x^2}(x>4)`
`=x-4+\sqrt{x^2-2.x.4+4^2}`
`=x-4+\sqrt{(x-4)^2}`
`=x-4+|x-4|`
`=x-4+x-4(x>4=>x-4>0)`
`=2x-8`
