Bài làm :
a,
`A=2\sqrt{x}-3\sqrt{x}-\sqrt{25x}` `(x>=0)`
`A=2\sqrt{x}-3\sqrt{x}-\sqrt{5^2 .x}`
`A=2\sqrt{x}-3\sqrt{x}-5\sqrt{x}`
`A=(2-3-5)\sqrt{x}`
`A=-6\sqrt{x}`
$\\$
b,
`B=\sqrt{25x-25}-\sqrt{9x-9}+\sqrt{4x-4}` `(x>=1)`
`B=\sqrt{25(x-1)}-\sqrt{9(x-1)}+\sqrt{4(x-1)}`
`B=\sqrt{5^2 . (x-1)}-\sqrt{3^2 . (x-1)}+\sqrt{2^2 . (x-1)}`
`B=5\sqrt{x-1}-3\sqrt{ x-1}+2\sqrt{ x-1}`
`B=(5-3+2)\sqrt{x-1}`
`B=4\sqrt{x-1}`
c,
`C=(x^2-2x)/(x-2)` `(x \ne 2)`
`C=(x(x-2))/(x-2)`
`C=x`
d,
`D=(a-2\sqrt{a})/(\sqrt{a}-2)` `(a>=0 ; a \ne 4)`
`D=(\sqrt{a}(\sqrt{a}-2))/(\sqrt{a}-2)`
`D=\sqrt{a}`
